i'm using interfolio, no, it's not necessary.
it seems efficient and easy on the writer (they only need to send one letter to one address, and don't have to wait for matching form to send).
unless you're only applying to a few schools, it's not much more expensive. you can have interfolio send all of your letters/matching forms to AADSAS in one bundle (=$5).
the electronic letter submission seems like it could pose some problems (electronic signatures and whatnot), but as with electronic AADSAS letter submission, it's not necessary.
also, worst case scenario, you don't get in this cycle, interfolio saves your letters and you won't have to bother your writers again when you apply in the future.