G'day Tinus,
I've been an Altium user for 3 years, but last week I got a job as a PCB designer. My new employer is an established defense contractor, who use Mentor.
So, on Wednesday, I got my first taste of Expedition... it is clunky compared to Altium, but MAN, it's crazy powerful. Maybe too powerful for simpler boards, but if you're doing RF work a lot (as we are), it just has all the integrated tools to handle RF and high speed work.
I've been plugging along on my own, asking my colleagues the odd question, and I think I'm getting the hang of it pretty quick! Training might be useful if you need to get up to speed quickly.
Honestly, if you need the capabilities, and can handle the expense of he license, you'll love Mentor. Just give yourself a month.
Cheers,
Pete