Update: canned the ST and started looking at BOSS Micro BR and the Line 6 Pocket Pod. Thanks to the guys who suggested these.
As with restaurant orders and anything else requiring a decision I went all "funny" in the guitar shop and purchased something totally different than I came for.
I'm now the proud(ish) owner of a Vox AC30 Amplug - sadly it's exactly like an AC30 ...when setup the WRONG way to get a great tone!!! Augh!!!
Yes it sounds like an AC30... with both bass and treble turned up and cut full up as well. Gritty bitey harsh rattly clangy nasty... sigh... this is the default crap sound - you can turn it up or down make it boomy or ice-picky - but ya can't fix it with the three controls provided...
Now... I'm suspicious my senheiser head phones may have drawn more current than the poor little bugger could supply, there was no way to get a thump out of muted strings or any warm bass... low voltage maybe? high current draw? ... so next stop is some pluggy earphones and pair of fresh batteries.
I'm an optimist - so more later...
Update: so the more later is - proper earbuds and fresh batteries make a big difference but still nowhere near my idea of a good AC30 tone.
I'm guessing that the harshness might be "not too bad" when you play along with a backing track - next port of call shall be - try that...