I really only have 1 problem with this, and it's a pretty major one I'm surprised no-ones picked up on yet:
You have them listed as a Fast Attack option which they are really, really not in any way shape or form at all whatsoever.
If they HAD to be mounted in the transport, then they would be
FA, if they were jump troops or bike / mounted troops again they would be, but these are Troops or
maybe Elites / Heavy support, they certainly don't fill a
FA slot.
Oh - and BS4 could in theory be explained away by the advanced tau tech giving them that 1 point
BS boost.
Also - you have to bear in mind your average guardsmans statline, and cost. I'd personally switch it to something like: