Here's why:
1) Cheap oil line fittings. Yes, they are NOT Earl's, Russell, Aero, or XPR. They are extremely poorly manufactured. I have held these side-by-side with the real deal and it's scary. The machining is horrible and not straight and these WILL leak and WILL cause your turbo to fail.
2) Crappy couplers. I bought a single coupler from eBay to compare with Brand Name 5 layer silicone couplers. I think the layers are non existent as these look like a single rubber piece. Good luck trying to add boost and having one of these blow off or apart.
This is a hit or miss thing. I've used no brand couplers with 0 issues on moderate boost/power levels. I have blown apart every single no brand coupler on the car now that I upped the boost to 24psi. If you intend to run large power or just want maximum reliability stick to name brand Samco etc
3) Crappy, fake, unreliable turbo. The turbo is no-name. No specs are given, ever. Just a bunch of supposed specs without any flow rates, dyno's, etc. It is cheap and will fail, guaranteed. It will not spool NOR make good power NOR be reliable.
Correct, the big doozey here is spool time. on the vw forums people have shown that the exact same size/spec turbo from a name brand place (bullseye, precision, garret, turbonetics) will spool almost a full 1000 RPMS sooner.
4) Knockoff Wastegates and Blowoff Valves. Some say these are fine to be cheap on, esp the BOV. If you buy a cheap fake BOV or WG and spend thousands on a kit, why cheap out now and get inferior products? What is another $100 when you've spent $3-4,000? Get a real WG and BOV and save yourself from problems later on when these fail.
5) Crappy intercooler. Some will say the intercooler is great. How do you know this? Do you have a picture of the intercooler from the inside of the hose end connectors to show how the fins are arranged to actually show it will flow and cool? You don't, nor do they ever show these pics, nor post how efficient the intercoolers are.
I'll try to find the flow tests on some of these but its pretty common to hear that the ebay godspeed cores are fine for a 300whp or less build you can compensate for the slightly less efficient core compared to a name brand by getting a slightly large off brand.
6) Intercooler piping is universal and won't fit. None of the pipes will fit the focus. They are pre-made sizes. You will have to spend hundreds to make them fit and you'll more than likely need more piping.
6) Oil (feed) lines are crappy. I've had one of these fake ones. It's scary. Not flexible at all, very long and will not fit well or look good. The connector ends are cheap and just like the hose fittings, horrible cast and WILL LEAK. The line ends are also crimp so there is no way to shorten the line if need be. You will have to make your own line to have a proper one.
7) No oil return. How are you going to return the oil to the oil pan or block? You don't have an oil pan with a bung nor taps for the block to make one.
8) Gauges are completely crappy. No brand gauges. I wouldn't trust these to be accurate, look good or perform in any way shape or form.
EXACTLY gauges are the life monitor system of your car. if you dont have reliable gauges you have no clue of the true status of your car.
9) Downpipe sucks. All of the parts are mild steel. They WILL crack. That nice silver shine will go away fast.
Not true, most of these are stainless and hold up pretty well. the jetta had a ebay downpipe all summer long and I had absolutely no issues with it.
10) Oil catch can is a joke. No baffle, nor will they tell you info on it. If it has a "baffle" it will consist of a sponge inside the car. Really now, a sponge?
11) No air filter. How are you going to protect the turbo from sucking crap in? You won't because you dont have a filter nor a connector to it in many cases, nor will this fit.
since its a "custom" kit with end user deciding the placement it doesnt make sense to include an air filter because how are they to know the size limitations of where you are placing it?
There is more but that's it for now!!