1. Fit is very important. Suit should be very snug on land, comfortably snug in the water. Strangulation is bad. There are differences in constuction, fit, durability, etc., between some of the cheapest tri-specific wetsuits and the next steps up. IMO, you may be better served by spending a bit more here, but no need to go top of the line unless you really want to.

2. Look for tri-specific brands. I like Orca. Others like De Soto, Ironman/Blue70, QR, etc. These should all be designed with more buoyancy in areas that benefit freestyle swimmers as well as better hydrodynamics, versus the less specific design and less tight fit of a surf suit or a dive suit.

3. Real benefits are speed for slower swimmers, buoyancy for everyone, and insulation in cold water. Buoyancy is key. If you are a strong swimmer, your times may not improve much with a suit, but you should save at least some energy because the suit does so much of the work of keeping your body in a good position. I'm a relatively slow swimmer, and I can measure a roughly 20% time improvement swimming with the same PE level in a wetsuit versus without one. Plus I feel fresher for the subsequent bike & run. Bottom line: if the race is wetsuit legal, I'm wearing my wetsuit.