Yates Shorty Screamer arrived. It's almost 7" end to end and 2.04 oz. I just took it out of the package and haven't loaded it yet, so it may stretch a little more. But at this length its in the same range as the 20cm Petzl Sorber. Using a typical caribiner to include it in the system its a net add of roughly 10".
In general it looks really good, definitely clean and compact, should pack easily with the rest of my kit.
As you can see in the provided paperwork snaps the Shorty model is intended for Fall Factor .25 - 1.0. and is supposed to activate at > 2Kn.
My intended use is on my tether attached to a secondary bridge on my linesman loops to backup my SRT/RAD climbing system. In this application depending on whether I tend the tether after each pull on the ascender or not I should never have more than 6"-12" of slack on roughly 30" of tether.
Maybe some of the propeller heads on here can sanity check me on this, but I'm calculating my rope segment of the FF formula as the length of tether where it exits the girth hitch eye at the trunk, plus the friction hitch length to the caribiner that attaches to the Shorty from its place on the tether. In reality there is probably some shock absorption from the length of tether constricting around the trunk, plus some stretch or creep of the friction hitch on the tether as it comes tight, but I think its safer to assume those are zero.
So using my estimates a fall factor with 6" of slack is .2, 12" = .4, 15" = .5 and so on.
In any event, as long as I'm advancing my tether to head height or above as I ascend I'm never falling from above my girth hitch attachment point, which keeps me below a FF of 1. Well within the Shorty's effective range.
Unless something comes up I'm going to try to hunt this afternoon and will give this thing a try and report back, hopefully with a hero shot too.