I suppose the answer depends a lot on what sort of modeller you are. For me, a loco is merely the means by which I can get my hands on a chassis which I can bash into something more appropriate for my railway. I can't really justify running a Stainz on my line as I want a small fleet of UK-built locos - though some UK NG railways did run O&K locos and a few Baldwins popped up here and there on UK railways. I do have one Stainz left over from my Starter Set but I'll probably get rid of it cos, although the chassis is robust and the valve gear is useful, I find that traction tyre a bloomin nuisance. I've removed it but the loco still doesn't run anywhere near as well as my Otto based locos which don't have traction tyres.
Rik