I didn't make a simple list of the brand names that I trusted before. Here it is.
Valve's and T's (& tubing) $30 John Guest
Filter 1 $10 MatrikX
Filter 2 $10 MatrikX
Filter 3 $15 MatrikX
Filter 4 $15 Omnipure
Membrane $40 Filmtec
Flow restrictor $15
Permeate Pump $45 Aquatec
"90%" cut-off valve $15 Hydronamic
4 Gallon Tank $70 ROPRO
Faucet $30 Touch-Flo
TDS meter $15 Hana
Flow meter $30 DigiFlow
Filter housing $60
check valve $7 (instead of air-gap faucet)
The price were a while ago. Google manufacturer's name or on eBay, so you get good price. From time to time, people just buy in bulk and sell them separately on eBay close to wholesale price but still make a profit. It's difficult to bait and switch and I think it's impossible to have fake items.
To see what you get for $390 see this Flomatic system I just came across. It's completely NSF certified (like mine) and it looks very much like my system (and any other system) except for the integration (to save labor cost for them probably). However, there is no pump, so the performance is inferior and probably the filters and membrane are not the best.
John Guest is the patented name of the tubing connection system and also the manufacturer of a few things. JG is the easiest system - leak proof. Valve is important because I told you before Lowes sell valves near ice maker tubings that carries a health warning. JG is NSF certified. All it's valves come with a beautifully fine JG symbol on it. You need a very fine plastic moulding process to copy that. If you have the tech and money to imitate it or fake it, you should have done a lot of other things than making some valves. JG make tubings too, though you can also find NSF certified tubings in hardware stores.
MatrikX filters are well known and well established, certified. Also a solid piece of work holding in your hands. The paper labels are well printed and now there are trademarks moulded on the filter housing, if I remembered correctly. Again if you can make that solid piece of fine work, so heavy, for $10, you can make a lot of other things to make money. Prefilters are for chlorine absorption to protect the membrane, though you can add some fancy filtering capabilities. Since my TDS readings are the same when the filters are new and a few years later, they are working as they should.
Omnipure is similar. MatrikX is the master of block carbon for prefilters, while Ominpure is the master of granular carbon for post filter - not for chlorine absorption. I think it's there to eliminate the taste due to bladder in the tank, at least my 1st cheap tank. Fine labels are printed directly on the housing.
Flow restricter doesn't matter because it's on the brine (waste water) path. But you do need to have the correct flow rate to match your membrane.
There is only one manufacturer for the permeate pump, Aquatec, who also makes a lot of other electric pumps for years. It's a certified component. The pump is completely sealed in tough plastic. The protective plastic doesn't look beautiful but it works - I measured the pressure and TDS. Not anybody can make something like that work - on and on 24/7/52. The smaller one is quiet but limited to 50 gpd and below (check).
The "90%" automatic cutoff valve from Hydronamic is a bit of mystery. They make a lot of other conventional RO valves with typically 60% cutoff. I bet they have some certified 60% valves but I didn't remember if I checked. It's has been a while now but the 90% valve is still not on their website while others are there. But there are no other valves like that on the market. There are controversy about the run away of the term 90%. They aren't - I talked to the manufacturer. But it's not really their fault because they don't sell retail. They do promise to check my valve and replace it if it doesn't goes up to 85%. But I changed my mind about it. Firstly, the value shouldn't relate to water quality - the pump make sure of that by isolating the two parts. The tank should fill more due to higher pressure but 4Gal is more than enough for me - there's no smaller one. I have at least 70 psi input feed, 90% gives 63 psi, higher than most people's main water pressure! My valve is probably 70%, a lot lower than 85% but at 50 psi it's supposed to be the standard main pressure! Conventional 50% valve doesn't have anything wrong in them. But now I know some fridge need 30 psi for ice maker. So you need at least 50 psi at the input.
ROPRO tank makes the others look like toys. It's certified, indestructible, beautiful and space saving. If you stand it upright, make sure your cabinet can stand the pressure, 4 gal per 9" diameter. You can stand it sideways or anyway you want. My 1st metal tank dented, chipped, and leak air. I need to pump it like a tire once a while near the end, and water smell of rubber. Never need to do anything about the ROPRO. The name is mounded on the housing. Actually I wanted to buy a certified metal tank to save money but the retailer give me this for the same price. I bet he didn't sell inferior metal tanks anymore and ran out of stock.
Everybody use Touch-flo faucet because any designer faucet cost $100 to hundreds. Touch-flo's are certified. Now they comes with tubings attached so you save a lot of terrible work at the deepest corners under the sink. The ones I got do not have markings on the faucet because most OEM's use them. They are sold in complete systems by other manufacturers - with or without their brand names etched on the faucet. Forget about air-gap - they can be very noisy and you need extra tubing and connections. It's the same as the air-gap on your dish washer. Just add a check valve so when your kitchen sink blocks, the waste water won't go back to foul your drinking water. I don't think it's a real problem, as long as you remember to disconnect the brine tube from the kitchen sink drain, like a manual on-off valve, before you pour poisonous drain cleaning chemicals down the drain.
Get a TDS meter, so you installation is fail safe. You can't get 95% TDS rejection any other way.
Flowmeter is rather new, in a form suitable for RO systems, monitoring a few different filters and tell you when to change it if you input sufficient data. I haven't tried it. It's rather bulky, a box stick to the front of you system with 3/4" connector. But I think replacing one of the 3 prefilter housing with this will make more sense. It's not certified I think but it claims they use certified material. That's very true, as long as they use certified plastic in contact with drinking water, it should be OK. That goes for the filter housing too. I don't think you can get branded name housing with NSF certification at a good price. But really it's a piece of plastic - if they use appropriate material, and the mold is fine and doesn't leak, how wrong can it be?