I use the Louis Garneau moldable and the Specialized BG footbed. The BG is used in my road shoes, and the Louis Garneau works great in the MTB shoes. The Garneau feels better overall, however and I would put them in the road shoes too if I didn't have the BGs. It makes the shoes feel custom and has prevented those dreaded hotspots that can ruin a great ride.

The Garneau was easy to heat and easy to set by standing on them in the shoes for a few minutes while they cooled. Once done, my already comfy Shimano WM80s felt even better. I bough the blue 'cool' ones, as out in So Cal it rarely gets cold enough to need anything insulated in the shoes (and I can always wear shoe covers if it gets cold).

Sorry, I have no experience with the Sole Slims.