They are a strange size - mostly 1/26 - 127 ish (exact scale depends on the bit of the loco you measure), so oversized for gauge one (the taurus is actually a standard gauge loco), and under for metre and other narrow gauges. Intention behind this strange choice which is also used for the rest of Piko european range and things like LGB V200 diesel is that it'll look OK mixing it with 'proper' narrow gauge stuff. Similar idea is behind all the 1/29 US stock from Aristo and USA, because US trains are so big, they use a smaller scale to make the same size models.
So you can run your taurus on a LGB RhB sliding wall vans and 1/29 boxcars, and at first glance it looks as though they're a train in a consistent scale. Compared to 1/32 or 210mm gauge one, it's WAY oversized, but fits in nicely as a sort of semi-freelance engine in the RhB mold
I've got one of the locos and mechanically they seem nice and tough (pantographs can be broken but they're aren't too fragile), but I don't have that much track, so maybe someone who's got a loco with more miles on it woulb be able to say more.
J.