Highz: I'm looking more to add than switch. If your a "pack in" sort of fisher person and/or the water bodies you're targeting are modest the tube style platforms are a good way to go. In my "BC"(Before Children)days I used a belly boat or round style tube I backpacked all over with good results. I now have a couple Caddis round tubes and a Creek Co. U Boat. An interesting thing about about one's offspring also being one's fishing partners. Once they catch on to the activity they expect to be outfitted as well as you are. The reason I went to a U Boat is #1 it was on sale #2 it's a lot easier to get into, out of, sit in and #3 it seems to me easier to maneuver and hold in one spot but that may just be me. My oldest, (15yo) partner can drive a round tube around like a sports car. I should mention that U Boat, while Creek Co.'s model name, it's also generic for that style of tube. A final advantage of a float tube is they are easier to haul around in general.
I'm looking to add a pontoon setup to the flotilla to do some river fishing. Here in Eastern Ore. there are a some places I fish that the current is more than I want to take on in a tube, but people do on pontoons all the time. That and while I can both fly and spinner cast fine from my tube, some pontoons have a platform one can stand up and cast from. I think this should make sight casting to fish mucho easier.
In closing I can say that I've caught more fish because of the access tubing has given me. I don't anticipate that changing with a pontoon setup. If your considering a purchase both camps have a cult like following, thus as usual the internet has loads of info and good luck with your decision.
Don't know what I'll do if I get a pontoon and the partners decide they need to upgrade also. Tell them find a job I guess....