For those of you who are on the fence about upgrading to 4.5.621 this may be just the thing to push you over the edge! There are many reasons to upgrade to .621 as this was a huge bug fixer! The big reason not to update is the fact that Motorola has disabled the ability to downgrade with their sig checks. Rootzwiki user KY41083 has compiled some prerooted builds of 4.5.621 that are flashable via CWM Recovery. However if you flash any of these you will be forever stuck on 621. If you soft brick your phone and require an SBF your only options will be the .604 Milestone SBF or the .621 SBF. You will not be able to downgrade to .605. If you must flash this ... proceed with Caution.