SUP fishing rocks...you get in amazing shape while fishing (oxymoron) and you can totally sneak up on fish and catch ridiculous numbers. It's definitely one of my favourite methods to fish for summer bass and pike. You're gonna have a blast! Just make sure to get out a lot on flat water first, and get comfortable with your paddling. Of course if you buy an iSUP designed for fishing, it will be much more stable than an all-around shape.
I haven't done much fishing off my iSUPs, I always prefer to take a solid board out.
Having said that, I've taken my C4 Waterman ATB inflatable down some very long stretches of river, with lots of portaging and shallow/rocky sections, solo with no cellphone. So certain makes/models are built quite strong.
But having been in the business for years, I've seen my fair share of inflatable SUP problems, that have gradually waned my confidence in risky expeditions on the iSUPs. In the past I would go for a winter paddle without a wetsuit on an inflatable. Now, I wouldn't do it, even if on an ULI (which are the pioneers in this space, and are the only brand making their boards in North America.)
That means virtually every other brand is manufacturing in China. A lot of these factories are like the wild west. Quality control can be sketchy. For maximum strength, ULI, C4 Waterman, and possibly Badfish come to mind as reliable brands.
Last summer, I sold close to 500 inflatable sups throughout Canada. Of all of those boards, one of them developed a bubble on the seam and popped, and one customer called back shortly after his purchase, that his board had exploded.
The one with the popped seam, was left inflated at full pressure (15PSI) from April until August, when it bubbled in a small spot and popped. It was left outdoors 24/7, in the sun, and the board was largely black. So although disappointing, it was not surprising. The lesson was not to leave them inflated all of the time, and to avoid storage in direct sunlight, especially for black boards.
As for the customer whose board exploded, I was mystified that all he wanted was a replacement. Why didn't he seek a refund? It was fairly obvious that he caused the explosion, likely by hooking the board up to a large air compressor and putting way too much air in there. If the thing exploded out of nowhere 1 week after buying it, clearly he would have been angry and wanting his money back, and scared shitless to ever use one again!
So 1 or 2 "defects" out of 500 boards is not bad. But since you'll usually have at least $300 worth of tackle on board, the thought of losing it all makes me want to stick with hard boards for fishing.