I have been learning about this first hand since December, after having ordered a Trampa spur gear drive complete. Previously only worked with belt motors.
Like with most things in life, each has trade offs. The mentioned pros and cons are not off, but there are a few points I’d like to add that were not so obvious getting into gear drives.
Better torque and acceleration for sure! Helical beats belts on this like no other.
Efficiency is going to depend on the gearing and wheel set up used. Gear drives don’t usually come with the same range of gear ratios to play with as belts.
Less maintenance - this is veeerry debatable imo. Have had to do so much adjustment and upkeep with the backlash, that it ends up being similar. The difference is that you may do less work over time with gears, but when you do have to do work on it, it takes a lot more work and mess to deal with. With belts, you will wear and run through belts, but the ease of changing/adjusting belts is something to consider over grease covered gears and housings. Also if a pulley in a helical drive gets damaged on a ride, much harder to deal with than a broken belt. As mentioned, this is really a matter of trade offs and perception/preference.
Less rolling resistance - questionable as it depends on how tight you run your belts normally. If you ride streets with descent pavement mostly, then you can afford to run your belts a little looser and roll resistance is not so bad. Someone riding with a lot of hills and bad streets may need to run things a bit tighter, to account for braking and belt slippage.
Cost and weight - this really depends on the set ups you are considering and may vary if you consider other makers. I believe I recall Trampa’s open belt drive is slightly more heavy than their helical gear drive. Cost on the other hand will depend on how many features you want (like belt tension pulley or bashguards) vs “good enough”. The IdeaTB’s is really nice and compact, but if you want hit trails, an enclosed system would be best.
Slightly louder - would change this to definitely louder. The difference in amount of head turns from people when riding each is obvious, not for a quite ride by any means.
When there is a problem with a gear drive, there is a good amount of work to do. Belt drives are a bit simpler and currently the most used, so there is a lot more folk to ask questions. There have been times when my Trampa has just sat in my work area, because its basically a big project to work on and requires time+dedication.
In the end: I love both set ups. Helical for power, responsiveness, and hill climbing, and how it makes my belt drive seem a little wimpy at times.
My belt set ups are more for casual, carvey, and commuter style rides. (not to say you can’t do a bit of each with both).
Honestly, I would say if you love to eskate and can afford to, go with having both eventually. The ability to choose your ride based on needs/use, is simply the best way to go in the end. Etoxx makes some of the nicest drive systems in the DIY scene and you likely would not be disappointed.
Exception: If you are a commuter looking at owning 1 good quality board for the time being, go with a belt system, as they are much easier to repair on the road if needed.