Yeah, Tiga's form changes were a really simple effect. Which is a good thing, really. When they tried more flashy form-changing with Dyna, the CG was rather crappy. They actually had a completely CG Ultraman Dyna during the form change sequences. Wish they just used something simpler. I think some episodes simply had a big light appear and Dyna already in a different form in the next shot, At least episode 31.
Back to Kuuga: I prefer DCD Kuuga's style with Henshin and form-changing. It wasn't a CGI model of the suit, but actual images of it. At least, that's what it looked like to me. Looks nicer and smoother.