I have a SlingBox 350 and a Hava HD which is the predecessor to the Vulkano. The Hava HD is only SD and from the PC program does provide good quality. But the viewing from the Slingbox350 blows away the quality of the HavaHD/Vulkano with their tablet and phone apps, even though it's still SD on those devices. The PC app for the Slingbox will show it in HD though. And you can get HD from the Boxee Box Slingbox app too.
But if I were getting something and didn't already have the SLingBox and Hava, I would either wait for the mini or get something cheap to tide me over until the mini is released. If you can find a Hava HD for only $60 or so (I paid around that for mine over 3 years ago from Woot!) and you have a PC at the TV, you could use that for now until the TiVo Mini is released. Otherwise the Slingbox 350 retails for $180 which is a little high.
TiVo Mini x4
Roamio Basic OTA
53TB unRAID2--38TB unRAID3--33TB unRAID1a