I used to have a Polycraft 4.55 but there aren't many of the 4.50 models around.
The main differences are that the rear pods on the 4.55 have been shortened, the front compartments under the front deck have improved doors and access, the rear seats have been squared off and and storage is available under them.
Pretty much all comments applicable to the 4.55 apply to the 4.50 other than those listed above. Do NOT buy one with 40 horses on the back, polys are heavy boats and the 4.5/4.55 should have a listed minimum power of 50ps, try and get one with a 60 on the back.
They are a softer riding and quieter boat than pressed tinnies but not as soft as the best fibre glass hulls in the same length and they tend to throw around the spray a bit in chopped up seas. They are very stable for their length, boast level flotation, have a durability unmatched by either tin or fibre glass and the purchase price is cheaper than many other boats. Fitting accessories isn't as easy as with tinnies and side pockets aren't.
Ummm that's all that comes to mind at the moment...