Highly recommended. I have a few Martinis - one is from the Nepal Cache being sold by IMA.
They are a bit of a project - first to disassemble and clean/repair the gun, then the even bigger challenge of getting it firing.
Luckily, many have gone before you, so there is a lot of help, do a search on "British Militaria Forums" and you will find entire forums focused on Martinis as well as other British arms like the Snider.
If you already reload and cast, getting into these is not a big deal. Lee makes affordable dies, and guys on the forum sell the formed brass.
If you buy from IMA, I'd recommend the Mk IV as they are in better condition. The Mk IV also takes a sword bayonet which is awesome and worth getting in a package deal if you're into that kind of thing.
If you need any help PM me. We have New England Victorian Riflemen shoots on occasion.
This is me shooting my Braendlin Armoury Commercial Martini Carbine in 577/450
and this is the opening volley of the Victorian Riflemen at an annual shoot
[video=youtube_share;rFqQWuaOGR4]http://youtu.be/rFqQWuaOGR4[/video]