It's easy for me to say this as a gamepad reviewer who has never tried to make one, but I really don't think designing a great mobile controller is that difficult. So many brands have tried, but they've focused way too much on portability, or making it feel bespoke to a phone, or trying to fill really niche areas in the market that haven't been catered to yet. It just doesn't need to be that complicated, and a simple, on-the-go mobile controller shouldn't cost the $160 some companies will charge you. Just take a regular-sized gamepad, cut it in half, and that should really be the end of it.
The ELO Vagabond seems like it understands all of this. Why downsize a regular controller when that will almost always hamstring comfort? Why charge so much when this is almost always going to be a secondary peripheral people won't have a massive budget for? Why change the shape and design of controller grips that people have been enjoying for decades now?