I realise you mentioned the TM, but I’ve got a Gen 2 Umarex/VFC which has been running like a train since I got it. It’s probably had 10k rounds through it totally stock, and apart from the stock catch needing replacing (common fault as the metal used is pants, but the replacement is steel and costs very little). There were some teething issues on the first version, but the Gen 2’s are solid.
Gas efficiency is solid, with a fill giving about two to three mags before needing to be refilled. In -5°C it was still running crisply on semi with Ultrair. The Gen 2’s come with an NPAS installed so you can tune it to the conditions too.
As an added bonus the VFC is 1:1 whereas the TM’s aren’t.