An interesting but difficult question. I don't think there are any cacti that are hardy and (relatively) fast-growing and without too many spines. How about Aloiampelos striatula?

I think it looks a lot like my Tunilla minuscula, not the easiest group of plant to ID though.

Oops, I was pretty far from the correct answer.
Good luck with you plant!

I am not sure, but it looks like cold damage to me. If it is, I think the plant will be allright, although marked, if you keep it warmer from now. The spots are probably hard? How cold has it been kept?

Mesa Garden has them on their list.

I am not sure .. but your plant looks like my M. lindsayi - which does not fit with what your label says - however it has a number of synonyms including M. sinforesensis and M. canelensis - not particularly close, I know, but it depends on how sure you are about 'reretensis'.

You might be interested in Cheryl Green and Dave Ferguson: Pricklypears commonly found in the United States and Northern Mexico. It's NOT a book about hybridizing though, more a little Opuntia lexicon. But it has a list of "Pricklypear ploidies" - or Opuntia chromosome count - as far as I ...

A very interesting discussion I found an alternative explanation to hooked spines. It may help the plant move to a more favourable position as it gets carried with debris after heavy rain. I have no idea whether this is a good explanation, I just read it here: https://en.wikipedia.org/wiki/Sclerocac...

I paid with visa.
Their homepage says that (outside of Germany) you can pay with credit card or COD (not sure what that is though), but I'd guess that means no paypal.

Mine arrived around the same time as those above, I think the 15th here in Denmark.
Thank you from me too.