Pluspunten
They'll find you a placement pretty quickly and seem eager to take just about anyone. How you find your experience depends entirely on where you're placed. My placement is great and I really enjoy working with the students I do. It feels like rewarding work. Good experience for people interested in going into teaching or working with youth in general.
Minpunten
There are a lot unfortunately. Be ready to get asked to do things beyond your contract (covering lessons, exam invigilation). Management depends on your placement, mine has been touch and go. Most people have no idea who you are because you're from an agency. Pay is crap, the advert is INTENTIONALLY MISLEADING. You do NOT get paid during holidays. They've found a workaround for this by saying that part of your daily rate is holiday pay in advance, which manages to not pay you for holiday and make your actual daily rate below minimum wage at the same time. Very clever of them. This is not a long-term job, you cannot live off the wage from this job by yourself. You'll also barely hear from SiT while you're on your placement unless they're reminding you to submit your timesheet for the millionth time. Even if you have a problem, they will acknowledge it and there will be absolutely no follow-up. You're on your own in the placement really, but in my case my colleagues have always been fantastic. Absolutely no real training, you'll be relying on colleague to tell you what you actually need to be doing.