Fibre IRS MK2 vs MK3

Hi all,

I'm somewhat new to the forum, it's been very helpful!

I was wondering if anyone could tell me the difference between the MK2 and MK3 IRS Quattro units? The specs look almost identical, but the MK2 are slightly more expensive than the newer MK3. Does anyone have any experience with these units, and what would you recommend between the two?

Thanks much