The older lockdown is good, but the new 'redesigned' one is even better. I have the old one and really like it. New one has a wide protective lid for the objective lenses, and the backstrap is modified to make it ride a bit more comfortably. Wouldnt hesitate to recomend the lockdown..
As for the Sidewinder/Evo - I would not recomend it. Its a great concept - and I used it last year during rifle season. I was worried about the quick detach and was always 'checking' to make sure it was there. In the excitement after I shot my elk, my rangefinder "quick detached" by itself somewhere in the Colorado sage flat. Fortunatly there was a foot of snow on the ground, and I was able to backtrack the next day and found my range finder.