we always seem to try to shortboardize the true fish instead of seeing how fast and fun they are,and everyone fell in love with the mini-simmons concept,though it is extremely limited and rarely ridden well.
first, to each their own. different people with different surfing styles like different boards. second, as mentioned, talk to local shaper. they may even let you try before you buy. my experience with a mini simmons:
they always intrigued me but i had a hard time buying as i never tried, luckily local shapers near me are super cool and one let me borrow one for a few weeks. i was sold after a few sessions. love my mini simmons for the right days. right days being thigh to waist, when you wanna switch it up from the longboard. plus some days i don't feel like strapping a log on the top of my jeep. simmons are small so easy to throw in your ride. i've taken it out in chest high and its still super fun, just set expectations though, its not going to perform like a thruster. the right simmons will be fast and fun to play around on. i will say though, it does take some getting used to. took me a bit to figure it out. i've tried keels fins on my 5"2 twin but not a fan, i like the bigger fins that give you a bit more drive. i've tried a bunch of fins and had the best luck with the True Ames 5.5" Twins
i'm a fan of alternative boards and local shapers, so keep that in mind. if you like name brands off the rack, thats probably your best bet.
My buddy just bought a mini simmons 5'10"x22"x3". He and I have both ridden in 2-5 ft conditions and it's held up fine. For small waves I'd really recommend the Proctor Lil Rascal or Lil Rascal 2, they are both a fish shape. They are insane in anything from 1-4ft maybe even 5ft, but it might get a little squirrelly. Check out Jay Phillips rippin a Lil Rascal at Malibu, it's effing crazy.