For off cuts less than about 12", then, yes, you do see a slight curve. But for cutting down an 8x4' sheet, both sides are very much usable.
For large shows, we get the DiBond precut by our supplier (factoring a certain amount of time to reject bad cuts...), on their panel saw - when the blade is new, the results can be great.
For smaller works, then we cut from stocks of 8x4 on the SteelTrak, and the results are good. Strangely, we can only get 3mm Dibond on a next day delivery - seems like 2mm has ben dropped in the UK...
We also have the Aluminium cutting head, but have never had any real joy with it.