Depends what you mean by 'career progression'. I flew with BA on longhaul for over 6 years and had a brilliant time, earning good money and seeing some great places, but personally, I didn't see myself loading beef meals down the back of a 747 or pressing 'brew' 30 times a flight as a career option. I've moved on within aviation, still getting the perks, but to a job that has developped my skills further than answering call bells at 3am and preparing endless trays of OJ!
I think you've got to try it, coldplay, as you will have a laugh and get to know about things only cabin crew experience (i.e the feeling of going on 2nd bunk rest on a Heathrow-Singapore or even the feeling of travelling in First class or Club when you've only paid pennies for your ticket!) but the job is a lot tougher now, normally minimum rest downroute and the salary has gone steadily downhill......and even allowances will be taxed in the UK from Nov this year, which means even less money.
Do it, see the world, have a laugh and then move on.