I placed an order for several puzzles from Creative Crafthouse in Florida a few weeks ago and they delivered some really well made wooden puzzles very quickly indeed. I can recommend them as a supplier, Dave is a pleasure to deal with.
My favourite puzzle that I received from them is the Muscle cube. It is available as a plain or a two tone version (I preferred the look of the 2 tone although I suspect that this version is made easier by the clues from the different colours). CC rate it as a very difficult or level 5 puzzle (on their scale up to 5+). I don't actually think it is that difficult - I would rate it a 3.5!
Despite this it is still a very pleasing puzzle to play with and is formed from a LOT of pieces which make a lovely, if disconcerting, pile!!
It has a single central key piece and from then on the rest comes apart systematically/sequentially. There are 33 pieces in all! There are 9 different types of pieces!
As I usually do, I was very careful to note what type of pieces were in each position and this made reassembly a bit of a breeze. It would have been much more of a challenge had I just disassembled it into a big pile of pieces and then tried to recreate it. I have learned from bitter experience that doing this is often a very bad idea but in this case the puzzle would be tough but not impossible with this approach (it would then justify the rating of 5).
The muscle cube looks great on the shelf and I have enjoyed playing with it - I can heartily recommend it to other collectors and certainly the Creative Crafthouse site is a delightful collection for all ages and skills.