Had a Tm mp7 GBBR for about 7 years, still completely stock internally other than the inner barrel and hop rubber (hop rubber was wear and tear)
mags can be leaky after a while, but gasket seal around the baseplate sorts this, all my original 6 mags work perfectly still , the 2 i bought a few years later are fine without any sealer,
range and accuracy has always been great, can compete with most full size rifles.
maintenance wise, it does need a clean every now and then, but once you get the hang of this its fairly simple.
ive used green gas and abbey Brut sniper gas for years with no issues, did run a couple of mags with propane right at the start, but it didn’t seem necessary
issues wise mine has a sleepy trigger thats only just turned up, haven't had it apart to check it out yet but should be easy enough to fix.
overall it has been a firm favourite for years, often I've chosen to use it instead of my Ghk for longer events,