I got curious and bit the bullet, here is a review.
I was considering using it a few days ago and the $5 fee put me off, but today I found out that 0.01 sign-up fee is credited to your account... So far so good. Making an account on Grams was problem-free and I liked the forced 2-FA.
Speed: you can load your Helix account after your fee payment gets 3 confirmations. After that it takes another 3 confirmations to be able to spend the coins you just loaded so all in all half an hour or so. Then you can choose a delay with which to execute the outgoing transaction and then the process, as they said, would take about 3 or 4 hours. Mine took 4 hours total, including a 2-hour delay, perhaps because the amount was small.
Taint: the ad is completely honest. Not only did blockchain analysis reveal 0 taint to my original address, but when I went to check up on the coins I sent to Grams - they all went to some internal address somewhere and the coins I got must have been new.
Now, there's a few important questions I cannot answer. Is /u/gramsadmin an FBI agent, trying to simplify his job and investigate every address to send him coins, as opposed to tirelessly wading through a sea of addresses that at some point inevitably end up contributing to market pool? Where do the fresh coins come from? More importantly, what do YOUR coins get used for later? Is there even a point to the whole tumbling thing if you don't know that? If /u/gramsadmin is not an FBI agent, will he end up getting caught and tried for money laundering seeing as he has a clearnet site up and probably some exchange accounts connected to Helix? Gah, I don't know.
For now all I can tell you is that Helix works, it works fast, and it works by giving you new coins as advertised.
Id like more specifics on this. You make it sound as if there is only one intermediate wallet. If so, thats a huge no-no in the tumbling world.
It doesnt matter if the coins are new if the process isnt done correctly. If you just deposit .5 btc from Wallet A to the Grams-owned Wallet B, and Wallet B simply deposits .5 btc to Wallet C, thats a shit tumbler. Useless, really. Pretty obvious Wallet A just gave .5 btc to Wallet C.