I can only speak from the experiences I have had in this area. Getting used to the plane after the likes of a warrior/arrow does take some time but if I understand correctly you have done the multi engine rating already ?what was this on ?
Rather than commiting to sending more money when you might not need to why not go with the flow I imagine the structure of your course is to...
10 hours FNPT ----- familiarise IR procedures (what a/c is this FNPT setup as ?)
10 hours PA28-R ---- Do IR for real in a slower a/c
15 hours FNPT ------ not sure why back to FNPT here unless its a senecca one and the one above was an arrow one ?
15 hours PA34 - the baby.
My personal concern would be continuity, make sure you can get it, how I have no idea but instructor availabilty, a/c availability, weather (get a weather making machine) ;-) etc etc