a) Slitting makes digestion easier. Some do it as standard practice for all feeds, some only do it when there's been a problem like a regurge. Just seems to help the process along.
b) Feeding tub - Yep, the main advantage is that they don't accidentally take on substrate with food. It also has the added advantage of allowing you free access to all of the viv and fittings, so that you can have a thorough spot-clean. Some have found that it prevents their hands being mistaken for food, when they're just going in to spot-clean while snakes are "at home".
As to the OP question of defrosting techniques, I either:
- Rest the mouse on paper on top of a radiator (winter months).
- Fire up a spare heatmat and pop the mouse on top for a few hours.