I haven't got the prospero transfer sheet, but i have found most GW transfers are difficult to work with compared to the Forgeworld transfers. I use a microsol/set equivalent even so.
It may be worth the investment to get a set from forgeworld.
I have both the FW and the BoP transfers, and I prefer the scarab design on the BoP ones. That said the other icons on the FW one are nice for variation on other units, especially the jackal, snake and falcon crests.
For BoP transfers I cut close to the design as possible, and pre cut relief cuts before taking the transfer off the paper. Make sure you gloss varnish the model a day in advance at least, as well. Next:
1. Boil water, pour it into a bowl
2. Drop cut out transfers in water
3. Wet the spot where you want to apply the transfer with the warm water - I use a brush
4. Pick up the transfer and apply - if your relief cuts are deep enough it will lie flat
5. Adjust positioning, smooth out excess water from the area
6. Let dry, then apply gloss varnish
If you try to make relief cuts while applying the transfer, I find it super fiddle. I always cut before dropping the transfer in water.
Never used Microsoft/microset before. I hear it works well, but the above works even for banners if you are careful to cut close to the design and do deep relief cuts