I have both XS20 and TH208, both have tune kits that have given them delrin guides, tophat and a TitanXS springs properly cut to size. I have used Maccari piston seals in both. The XS20 needed the Weihrauch trigger blade replacement to get a proper 2 stage trigger and feel, but £13 is peanuts for a trigger upgrade.
Both were bought new and at the right time to get a rock bottom price.
I've had the XS20 for 6 years, the basic gun cost £80. It cocks smooth as glass and shoots the same way and will produce a raggy hole at 30yds on superdomes
The TH208 is the copy of the RWS/Diana model 34 action but in an ambi thumbhole stock and cost £123, now being 3 years old. Very nearly a smooth as the XS20 and will produce equal accuracy with either AA Field or Crosman Ultra Mag. Both guns have barrel weights as standard, nothing clever here, just keeping the muzzle under control.
Both are .22 and the power is set by me so as to be legal with their respective most efficient pellets.
The fit and finish on both are more than acceptable irrespective of price, good but not great.
Spending £50 or so on a set of bespoke internals and a couple of hours of your time on a springer seems to be par for the course no matter what you bought or what you paid for it.
Both are going strong and neither has any "manufacturing issues" nor developed any fault.
Good guns, good price, as accurate as some and as good as most. At these prices, cleverer than they have any right to be.
Give them some halfway decent optics (both have Nikko Stirling Gold Crown Airking 4x12x42 AO) and they're a very competitive combination. They are not the quality of the guns they're modelled on but not that far removed and already performing just as well.