I don't think Tamim will cash much but Sakib certainly will/should.
And as we are under rating Ash,let me poin it out,Ash is the only BD batsman to hv scored 2 T20 international 50s whereas Tamim & Sakib(he got one in Wup vs Aus) are yet to score fifties.
So Ash is our most successful T20 batsman.
About County vs IPL ,I think as our T20 knowledge is very poor we need some of our plyrs to get some experience from IPL.
Tea20 is just not our cup of tea.