!I am a member of HSI but have yet to use. You can exchange a week through them, they will search for travel arrangements cheaper flights etc. ( I did utilize that service once), but all they could find at time I wanted was what I found myself, although they did respond and direct me to same site.
I own a few timeshares so my use of them is limited already vacation 10-12 weeks per year, but think they would be good option for those who only own one timeshare as they have burn weeks ( cheap but only 60 days out booking), then they have other offers 6 months out, would work out to be around the cost of a maintenance fee, possibly slightly lower or higher but no yearly MF committement.
So I think for some it could be a good option.....you can also place a request for an area or such and they will offer you resorts for your requested timeframe. I have done that but though was offered some deals I got an exchange for cheap and was giving away as a wedding gift, so ended up not utilizing their offers.
Their owners site has immense offers so may take some time to actually realize all the benefits etc.
Wish I could be more help. Good luck