The Red Mist will click fit into the 610 bracket but it is a stiff fit. You would think, therefore, that the 610 would be a loose fit in the Red Mist bracket but it is still fairly firm. I also tried an old Cateye 1100 in the Red Mist bracket, which was also a stiff but smooth click fit.
If you're not planning on regular removal, the brackets are effectively interchangeable but it could be a bit of a pain to remove every time you park up. The edge profile of the 610 'plug' end is quite rounded whereas that of the Red Mist is square, so some light sanding of the latter could improve things.
The Red Mist brightness appears to be identical to the 610. The only key differences appear to be a slightly lower quality power button and having it power off by stepping through the light patterns rather than a long press. Also, the batteries do not go in as smoothly as the Cateye - it's clearly a copy but not an exact one.
