[AtomicLabMonkey]

I've always hated the Detroit-80s-seatbelt style ones. With gloves on it can be hard to push the button in to release it, especially when the mechanism isn't brand new anymore. I'd go for something like a latch instead. Dimensions are hard to say, get it as wide as you can given your window opening length & sizes available to buy, and height is just determined by cage bars & net mounting details.