The dot is crisper than most other red dots I’ve used (Vortex, Trijicon, Redfield, Burris, Bushnell). It has a slight starburst effect but is better than most others, at least in my experience.
Yes, it is compatible with any Aimpoint H1/T1 style mount.
Yes, this has shake awake.
Yes, these Holosun red dots can use Aimpoint micro mounts.
The warranty is covered by Holosun's Limited Lifetime Warranty, which is 5 years on the glass/body and 3 years on the electronics.
As long as your receiver has the standard picatinny rail, this will mount to it with no additional parts needed.
I believe the "U" is a designation for the protected turrets.
It comes with a picatinny mount that allows for a lower 1/3 co-witness on an AR-15. For other mounting options please contact us at techsales@opticsplanet.com with the make, model, and caliber of the firearm you wish to mount this to.
They are essentially the same in appearance, but the M version is more rugged and has a higher water resistance.
That optic would be too tall, it is intended for use on a flat-top AR with a picatinny rail.
I don;t know what make or model of .357 you have, so I can't recommend a specific mount, but Weigand has some very robust mounts for popular revolvers:
http://www.jackweigand.com/
I would recommend something like the Burris FastFire II or III:
https://www.opticsplanet.com/s/fastfire?_iv_categories=red-dot-scopes
the Leupold DeltaPoint Pro is another excellent choice:
https://www.opticsplanet.com/leupold-deltapoint-pro-matte-7-5-moa-delta-dot-sight.html
Mark H.