Pros
Peripatetic shifts - you'll probably do a few shifts at one venue, then some at a different place, and so on. This builds up resilience and adaptability, and gets you into some cool places like tennis tournaments or the Grand Prix, or even Download Festival one time. Pay is usually good - 1 or 2 pounds above minimum wage. Management are pretty friendly, many of them used to do shift work before being promoted into admin roles, so they get it. Sometimes they work shifts alongside you. Most of the time lunch is provided on an 8 hour or above shift, but this isn't down to Off to Work, it's up to the venue they're contracting with. Not my chosen path, but if you want to advance to an administrative role within the company I think this is possible.
Cons
Of course, since you're going to new places every time, it can feel a bit alienating if you want to get to know coworkers better - although if you work enough shifts, you get to see some regulars. Long travel time to get to lots of venues - they'll provide a coach or driver, of course, or reimburse petrol expenses/train tickets. However, very rare to get paid for travel time (although this has happened once or twice). I say that management is generally understanding, but they can be merciless at times - for instance, overbooking the amount of staff they need for a very big shift (say, 30 staff or above with an important client), and then turning away anybody who arrives late, just to make sure they reach full capacity. In short, don't be late! If you're late to book shifts on the app, it can be very difficult to get work. There are also long dry periods, like January for instance, where it's hard to get any work at all. Seasonal work!