Velashape III or BTL Unison for tightening thighs?

I’m a 48 year old woman, petite and size 8. I’ve always been slim and firm but in the last year the skin on my thighs has become lax and saggy. I have grade 1 cellulite. I went to a dermatologist clinic and they recommended either velashape or BTL Unison. I don’t want any fat to melt, I only want skin tightening. Which is the best out of these two? I have also read comments from women on real self that velashape has given them thread veins. Is this really a side effect? Thanks