Jumping between instruments is fairly simple, but new mando players coming from fiddle usually have enough trouble figuring out what to do with the frets without adding greatly different stretch as an extra thing to get used to.

There's probably no sense in telling someone with a new instrument to "take it easy," but a first thing likely to pop up going from fiddle to mando is that after a fairly short session your fingers hurt. It takes a lot more pressure on the strings to fret them on a mando than fiddlers are accustomed to. If the mando only had one string instead of the double-courses, you'd slice your fingers off.

When ready to build up new callouses, good advice is to play for no more than 10 minutes or so, then come back after an hour. Repeat as needed, and you shouldn't ever get too sore to want to come back. In a day or so, your fingers will be ready for longer sessions.

A fringe "benefit" of mando vs fiddle - you can use a capo on a mandolin! This opens all kinds of new possibilities, good for countless senseless debates with friends (and possibly occasional real enemies). Whether you want to join the debate on the forem or 'ginem side will likely depend on how adept you were at high positions on the fiddle.

IF so inclined, on the mando you can also study up on chords, play bluegrass, and sound like a snare drum.

Mainly you can have a bit of fun.

John