No matter which tent you choose, if you have a vehicle to carry them, then buy a cheap plastic tarpaulin (as they are called) and a bundle of garden canes, a ball of good string and a dozen pegs.
If the festival is too sunny, it makes a shadehouse. If it is wet, you aren't confined to a small tent. If it is a total washout, drag that tent under it and use it for a fly.
Set it up like a ridge tent. You'll need some way of stopping the canes from sliding through the tarp grommets. Duct tape and washers?