Isn't multipool.us just a proxy to ghash.io for bitcoin/merged mining? The advantage, if there is one, would be the alt SHA256 mining when and if it is more profitable than bitcoin mining.
Yes we do proxy to cex.io/ghash.io for our bitcoin hashrate. That said, we only get a payout once per day (at the most) from cex.io, so the payout per GH has a little bit more variance than if you were to mine directly.
We've been on alts around 30% of the time over the past few days and we're beating pure BTC mining by about 10-20% on average.