Have you used these, what are your thoughts?

I don't have all of those in the picture, but my local cake supply had a set of 12 that I bought. My set does have a couple you show above. (could not pass them up for $25)  I have tried 2 so far, and I love them!  I did watch a few videos on YouTube and read up on them prior to using them, so that helped.  They are huge and I have a dedicated bag cut to their size (they do not fit on the large coupler, so keep that in mind). You will need to use at least an 18 inch piping bag for them, due to how big they are.  I used them for the top of a quarter sheet cake this weekend with a ton of leaves and they worked that way.  I think they would look good among other flowers as well, if doing a cake with different types of flowers.  I do think they need either other flowers or leaves around them otherwise I feel they look a bit odd. If you make them smaller that a full flower size, they could go on a cupcake (I think the full size flower looks too big on a cupcake).  I am still playing with them, but I like having them as a  quick buttercream flower option.   HTH!