I'll add that the fancy SRS-branded Albion bridles have a built-in keeper. (Yes, I have one. No, I bought it used; I'm not quite as crazy as I sound. The leather smells heavenly. I bought a Fulmer snaffle just for that bridle. )
Now that bridle sounds drool-worthy!!! DO you have a picture? I've never seen it up close.
There are pix of Podhajsky in Canada riding a chestnut (bred by my old teacher in Germany) in extension/si) and the horse has no keepers. (When he was here in 63 he addressed that.) I think at the srs there are a couple of things, the bridles and the keepers are handmade for each horse, and they have to allow for caveson use/in hand work. And keepers, today are virtually useless (too tight/short).
(For what it is worth, my mare wore no keepers with AH, and he agreed with the reasoning.)
I ride my OTTB in a single-jointed fulmer snaffle with no keepers and no noseband. My horse is much happier taking proper contact in this than a multitude of "gentler"/more popular bits and has no need for a noseband so I don't bother using one anymore (one less thing to clean or get hung up on the fulmer cheeks). I am extremely careful about not letting my horse rub her booted legs with her bridle on, but I would be equally careful with or without keepers. Keepers would significantly change the angle/action of the bit and they are not recommended by my trainer (or her trainer, PK) so I don't see any point to using them.
The first bit I ever bought , in 1975, was a Fulmer snaffle.This was on the advice of my instructor, an former British Army riding instructr who had spent time in Austria and had had lunge lessons from a young Herr Kottas.
I still have it , hanging on my Canadian's bridle - with keepers.
I never see them in the local tack stores, however....
I have a custom made (by Jay Shuttleworth) mullen mouth fulmer sided snaffle. Jay suggested the fulmer sides. I don't generally use keepers. I use a regular noseband that is quite loose. I love it, and use it daily
As far as the 'danger' aspect of full cheek bits, the hooks on any curb chain are at least as problematic. And the jumper riders certainly have enough other custom concoctions that are scarier looking.