As well as the shape, make sure you're getting the correct video support – native digital ones which are high quality but pricey, while the traditional analog usually has the ultimate in low latency for stunt pilots at the expense of low quality.
Some goggles include receivers and antennas, others just have places for them to be added. Be sure you’re getting what you need to communicate with your drone.
Other aspects to keep an eye out for are built-in DVR – and the resolution thereof – as well as the screen’s resolution and tech (LED is usually cheaper, LCOS in the middle, and OLED the best).