If you decide to go with the SPEC III - be prepared to make some modifications to the tank BEFORE starting it up - for the safety of your Betta.
The intake grid for the filter can/will shred your Betta's fins. Most of the users on the SPEC conversation thread have solved this by covering the intake grid with plastic needlepoint mesh sold at craft stores - ziptie it onto the grid and the holes are small enough to keep from shredding fins, but large enough to not impede the waterflow to the filter.
Secondly the filter output even with the pump set to the lowest will probably be way too powerful for your Betta and will toss him all over the tank. There are a couple of different modifications you can make to solve that (several actually, again see the SPEC thread on this list) the easiest and probably cheapest is to ziptie a Fluval Edge prefilter over the output nozzle to baffle the waterflow.
Finally the open hole in the center of the lid (for the light) also poses a couple of problems. If your room has low humidity you will have evaporation like crazy, and if you have an adventuresome Betta, you could come home to find him dead on the floor - there is more than enough room for a fish to jump out. Again many owners resort to covering the opening with craft mesh to prevent escape, but you will still be dealing with the evaporation issue.
I have a SPEC III, and after these modifications, it's a nice tank. Yes you can cycle it just fine, and if done properly you should be able to keep it stable. I got a second tank - a TopFin 2.6 gallon cube tank - way less costly, put a sponge filter in it, and I greatly prefer it over the SPEC. No need to modify filter, lid is entire, and the light (very similar to the light on the SPEC III) has a hinged base so you can flip it out of the way to access the tank rather than have to take it off to get to the entire tank.
Good luck with your new setup,
