We had one booked in the Peak District, after a load of (5 or 6) cancellations, then wife got pregnant, and they said you can’t go, and you’ll have to wait till next year, no refund. In the end we got money back minus 30 quid, and really had to argue with them to even get the refund, so check the refund policy. I wouldn’t bother booking one if you have any kind of a life, so can’t afford to waste a whole bunch of afternoon / evenings having to not go out in case they can fly.
Also, be aware some operators are more cavalier about the weather, so you may well find yourself cancelled, despite seeing balloons in the air.
Also, with the cancellation thing, at least with ours, it wasn’t a matter of come back next week, they fill up the bookings, so you have to wait for other people who booked after you to fly. by the time we got the refund, it was something like 6 months after my wife’s birthday when I’d originally booked.