Could it be that the sloop can handle blocks and lines that dangles along the mast better than the uni rigg?
Doesn't the snail system have a spi halyard hanging around the mast ?
If it does then why couldn't a similar setup be had with a normal snuffer ?
Afterall the spi halyard attached to the top when using a snuffer is actually in front of the forestay where as with the snail it will be near the mast as well.
I do find that the Sloop rig appears to be more forgiving with respect to Aerodynamic issues then a uni. But I think that is mostly because the uni rig is so sensitive to proper trim. A sloop keeps drawing even when slightly out of trim. In fact I feel that the sloop punishes off a mistake less severely and gives you enough time to steer back to the groove. Landyachting is actually even worse in this respect and as such a very good training for staying on the groove.
Wouter