This is my 2nd stint at Puregym, and on a whole, it's been a mostly enjoyable experience. Love the guys I work with but it's almost impossible to move into the management side of the company.
Be prepared to work anti-social shifts - you'll work anywhere between 6am and 10pm and this applies to Xmas Eve, Boxing Day, New Year's Eve, and New Year's Day. This place doesn't close at all and only guarantee you a single day off - Xmas Day.
Holiday's are few and far between - being self-employed you don't get paid anyway, but trying to arrange shift cover is a stressful task as it means other PT's working extra shifts to cover you and vice-versa. I've had 6 days off all year as I couldn't find cover for a morning shift.
Career progression is pretty much a non-event - it seems to be who you know rather than what you know. As one of the more experienced PT's who knows the company inside out and have been successful at running two PT businesses, I've been declined on a number of occasions for AGM/GM positions that come up. However, I've seen less experienced colleagues been given these positions. Plus PureGym tend to recruit their managers from outwith the company.
I would say PureGym is a good company to begin your career at, but if you're more experienced, do not use them to "enhance" your career/business.