I went to SGU and did the charter program 6-7 years ago (wow its been so long...) and I know it has changed some since then... It definitely is another business money grab but it will give you a running start so I think it could help some people who would otherwise struggle in 1st term. SGU has more "reputation" than ross but both are virtually equal in my opinion. I think Ross and SGU have better track records at getting their graduates into certain schools (my residency has a couple SGUs every year but no other carib's and there are some places with only Ross). I would look at the clinical rotation sites (SGU many sites in NYC/Jersey) , the course curriculum / schedule (differs at each) and factor in that 28K to make your decision. If you know what specialty you want you can also look at residency rosters at schools of your interest to see the proportion or Ross vs SGU. Also if you do the charter course in august remember that you wont start 1st term until January which means you will apply for residency with the class behind you... aka lose a year.
The Charter program probably doesn't do much for most students (those who do well would have done well in 1st term regardless) but it definitely will instill confidence. You learn the island, get used to the pace of med school, learn the school / etc.
I would make the right choice for you rather than worry about the 28K which really is nothing in the big scheme of things. Pick the place that will give you the best chance to succeed.