I'm wondering what the experience has been purchasing memberships this way. It sounds easy enough but wondering kind of results people have had, any feedback would be appreciated.

I have used them a couple of times. It set up a new acount each time but I contacted them and they credited the membership to my existing acount. There maybe a way to use them to pay into existing acount directly but I couldnt see it. They acted prety fast though once I contacted them

It's easy and anonymous.  Sometimes it takes a few hrs for the card to be redeemable.  

And have never had any problems whatsoever trading SBux gift cards for VIP.  Also, no issues at all with new accounts or anything like that.  I just sign in, click the appropriate links, enter the info, log out once it's done, log back in, and then boom I'm all set.