A few more thoughts on the 8099...

I find some of the clinometers unuseable with my nearsightedness and bifocals (the 8099 has multiple different clinometers). The hinge clinometer is fine. The 1 degree accuracy one that uses the "clinometer marking" on the backside of the baseplate is OK, about 90% perfect. The other ones that require you to read the hanging green arrow pointing at the green scale are impossible for me. This is an bifocal thing. Younger eyes or people that aren't so nearsighted possibly wouldn't have these problems. But how often do you use the clinometer, and how many different versions of the thing do you need on one compass?

The size of the mirror on the 8099 vs the size on the 15tdcl ... who cares? As long as the mirror is large enough to accurately align things. And it is on the 8099. No problem seeing the entire compass dial in the mirror. Bigger might be better for preening yourself, but it's not needed for compass functions. I also think the skinnier mirror on the 8099 might be easier to adjust the angle using a one-hand hold and your thumb. The full width mirror of the 15tdcl seems like it might be more awkward to hold and adjust one-handed (this is just speculation on my part). Using a compass mirror for signalling would be marginal at best. I always carry a seperate real signallying mirror anyway.

I'm not sure why the 8099 has two flip up covers. That does seem overly complex on first look. One guess is that this makes it easy to hold the compass and use your thumb to line up the marks to take a bearing. Only one hand is needed. The second cover isolates the turnable dial from the baseplate. Is this easy one-handed operation the same for the 15tdcl? I don't have a 15tdcl to test and comment on this.

As far a declination adjustment (screw vs friction), I'd just as soon have no adjustments at all. I really don't have a problem doing a little simple math in my head. I'd probably be more worried wondering if I'd remembered to pre-adjust declination or not.