I have noticed exactly zip zero nada changes in engine performance, idle is the same, driveability is the same no lag or dropping in power, in both the 1.9 and the 1.8 the only side effect is just a cleaner engine, it doesn't hurt valves, nothing, my 1.9 has bad rings because I screwed up and reseated my valves after I did the rings, woopsies live and learn! besides 2K miles on a fresh ring job then redoing valves the rings aren't even really seated yet lol.
but yeah I'm very well pleased with the catch can it doesn't mess up anything there's no unmetered air it just goes in line with the PCV valve to the intake that's it, and if you put it INSIDE the car it sounds like a BOV when you let off the gas and it makes a huge cloud in the jar ha ha! *don't ask* ok fine I tell, I put some gas in the jar to try and "vaporize" some gas and all it did was make the car run like poop, don't do that, just put the jar in there and take the oil out and you're golden guys! I recommend doing it to every car too, even if it's new, when you take it in for work just take the catch can out and put the stock hose and get work done then put it back to catch can!
doooooo ittttt!