The main concern with a Senegal is they are most likely wc imports that have not gotten perfect care. You could end up needing a vet to treat stress, dehydration, parasites and any injuries from all the shipping it's gone through before reaching the store. Senegals won't show as many dramatic color changes as veileds and yes, they are smaller. Not a bad thing necessarily. Stress shows in a pattern of small black dots over the background green. Their green is beautiful and they are underrated chams IMHO. If the cham is female most likely it is gravid...and you'll have to be prepared to deal with any eggs she might lay plus the risks of eggbinding. I haven't kept Senegals but have heard that they are pretty shy too.
But, if you like the appearance and personality of one that's most important...get the cham you really want rather than settle for something you won't be as interested in. Just be prepared to accept that there is less thorough husbandry information out there, that the cham might have unseen problems, and that it was probably taken out of the wild.