Measure the models diagonally, spanning the body from motor center to motor center. H, H-480, and H Pro are 480mm, the Plus is 520mm. The difference between H and H Pro lies in the RealSense module and having a an extra external antenna on the Pro's ST-16. H Plus uses an ST 16 controller that's visually the same but like the H Plus aircraft, is loaded with a completely different flight control system. H-480's and the Plus employ cameras and gimbals that cannot be swapped between them at this time. The H Plus camera is much better than H-480/H Pro. The various Typhoon H (480) model names describe the same basic aircraft. internally they are all the same, performance wise they are all the same, software wise they are all the same. Only RealSense makes a distinction between them, and the extra external antenna on the ST-16. Confusing that a little more is that Yuneec has shipped H Pro st-16's with H standard kit packages. No matter, they all perform the same.
Hopefully the guy that bought an H "Pro" without RealSense didn't pay an H Pro price. The money difference between H and Pro is all for the RealSense. Without RealSense the machine is a basic, standard, everyday Typhoon H.