Cassette stuck on a 3 speed internally geared hub. Generally works okay. I have one on a Cannondale that is grinding in 2 of 3 hub gears so it probably has a broken tooth in a planet gear and the busted off bit is stuck in the gears. But that's the only 1 I've ever seen with trouble. I've had hundreds of Sturmey Archer hubs apart, mostly for cleaning due to improper lube or abuse. And I've taken a few Shimano hubs apart mostly out of curiosity. But never had a SRAM hub apart. Just not that many around compared to SA & Shimano.
All the problems of an internally geared hub and all the problems of a derailleur system and both of the costs and weights. Add a triple crank and you have 3x3x8 (or 3x3x7) gear ratios. 72 or 63 gears! I think they got to 9 gears so 3x3x9 = 81 gears. I'm sure there would be some gear ratios so close you couldn't tell the difference. Shifting the igh can be much quicker than shifting chains from one cog/sprocket to another. Potential for a low gear lower than any other bike, high gear higher, etc. Depending on cog & ring sizes. More useful on a recumbent tadpole trike with a spare 100 pounds of load going up hill at 2 mph. Extra low gears allow for higher rpm to spare the knees.
Probably the biggest draw back is getting one of those low quality plastic SRAM derailleurs with it. The plastic derailleurs warp over time and SRAM rivets jockey wheels on so there is no servicing them. As they get dirty, they wear out and built up so much friction they barely function. IMO Shimano rapid fire shifters are vastly superior to any twist grip shifter and the mid to high end Shimano derailleurs are much better.
I have a Brompton with a 3x2 drive. 3 speed hub with 2 cogs and Brompton's own derailleur. Either shifts pretty quick in urban use.
The dual drive idea goes way back, like 70 years ago. There were kits for "English racer" 3 speed bikes that added 2 or 3 cogs to a 3 speed hub and had a simple derailleur. Cyclo & Benelux were two companys that sold them in the mid 20th century. They did not shift well.
One benefit of a igh is it's protected from bad weather. Well the derailleur and cogs aren't so that benefit is negated.
All modern igh hubs have input force limit specs. Some times listed in sprocket/cog ratios. Pedal way to hard and you can break the small gears in the hubs. There is the possibility of gear slipping if they aren't adjusted just right. I wound up in an emergency room because of one slipping on me. IMO, IGH hubs will bite back if you abuse them.
