Soundslice is an amazing tool to learn from in my opinion. I wish I would have had something like this when I was learning. It would have sped up the learning process for me no doubt about it.
I recently updated all of the Soundslices in the All Access Pass where you learn a solo to have two new files in the recordings menu at the bottom of the player.
This will give you access to seamless loops and also the ability to change between the backing track and performance with no lag. To me this is a great feature you can use to test how well you have learned any section of a solo.
To gain access to all of the Soundslices on the site check out the All Access Pass.