We have been customising Quicksilver heavy duty inflatables (SIBs) for years and we have done some pretty extensive things with them, to such an extent that people have mistaken them for RIBs and as the range goes all the way up to 5.3m they do look the part.
A SIB is...
+ Forgiving of being bumped and beached,
+ Easy to modify and then change back again,
+ Light, therefor faster or more economical,
+ Can be folded up after a holiday or end of the season*
+ Hold their value fairly well, because of that modular design.
- A shallow V hull (avoid anything with a flat bottom) so do not ride so well,
- Do not take engines bigger than about a 50, so will never be record breaking fast,
- Small gaps in the floor allow things to go missing,
A RIB is...
+ Robust, the GRP and Hypalon combination is mighty,
+ The GRP hulls come in many depths of V to suit all uses,
+ Easy to set up neatly, with cables below the deck and tidy permanent fixings,
+ One of the best boat designs ever.
- The good ones are often pricey, except old Seariders,
* With practice and some nifty tricks it is possible to assemble a SIB faster than launching and parking a trailer, so can be assembled per use if you feel the need.
There are more, but I am distracted.