Both Mal-Ec and I had Warranty replacements for the later model. I’m with Alec, new one is the variant the first one should have been! Mine’s done about 2200k in just over a year and the only issues has been a set of of replacement bearings and a DU bush. And it’s not had an easy life.
Not light for a 4.5in trail bike, but so a lot of fun to ride. No way I’d need a 5 (friend has one and it’s a hoot but I prefer my ST4) and the great thing about the ST4 is it’s great at most stuff I ride (FoD, Malverns, Wales, Trail centres, Peaks, Quantocks, etc).
710mm bars, bolt through fork, 2.25 tubeless tyres, 70mm step, dropper post and determined expression will get you up and down most stuff.
I’ve been a serial bike buyer for 10 years, but since having this ST4, not interested in anything else. Fab, love mine.