Given that they tried to make it accomodate most DSLR/mirrorless fisheyes, I think the design is decent, wouldn't be sure what else you could do to stabilise it further without making it a bitch to install/remove.
If it doesn't affect image quality during video and wobble too much when filming lines, then I'd say its a good investment, especially if you're filming with the Canon 8-15mm fisheye which is about $1000. Even if you have a regular 8mm DSLR fish, it could still be worth buying.
However, the way they're marketing it is strange, you can get close enough without the filter, any closer, and you're cutting off most the skater. They should just show it in action with regular clips, and demonstrate its protective function in the case of lens hits, which is what this is product should be for in the first place.