Some nice videos there Simon, better than those I have taken.
I have looked at the red dot finders Tony, and use one on our astronomy telescope.
I’m not sure how effective it would be in helping to video an aerobatic display ?

The best option is probably the loupe or hood which fixes over the LCD. This lets you see in daylight, focus,
and control zoom. I believe touching the shutter control while videoing will maintain focus. Although I
don’t know how easy they are to fit and remove, between taking video and stills.

Although The DSLR can give good results, on fast moving small aircraft you are fighting a losing battle.
I think that for shooting flying aircraft, a camcorder is the best bet as they are pretty inexpensive these days.
I still have an old Hitachi camcorder, now if I could convert that from tape to digital………..