Offering a Instant Play version (flash casino) these days is not a feature anymore its common standard for every casino. Instant play versions can look very different from brand to brand and that makes the only difference. The games in each Casino Software are the same but some casino manage to program more useful Instant Play verions than others.
The important thin is to access them from all PCs or Notefooks or even Tablets without any problems. There should not be the need to download or install a casino software. Sure downloading and installing a casino software has its advantages in speed and gameplay and has sometimes more features then an Instant Play version. But as long as you can play your favorite games without downloading a casino software it has done its job.
Flash, Instant Play