Yes they can be used without a brake, Blister confirms it in the comments here:
https://blisterreview.com/gear-revie...12-majesty-r12
If you want an aftermarket brake that would fit, you could definitely find one somewhere as the heel piece used in the Helio 350 is the same as the ATK Raider, Hagan Core, Moment Voyager, etc.
Before you buy from BD, I'd look into Spyderjon's prices for ATK. I have a Tier 1 pro deal with BD (not sure what the other levels are like) and Spyderjon's prices were similar when you factor in the tax you have to pay with BD, and he has a way better selection. I got really lucky with an industry connection to ATK but otherwise I would have bought from Spyder.