Some people find nethies to be high-strung, and with a tendency towards "little dog" syndrome (the whole trying to prove they are big and tough by being aggressive).
However, I have a big ol nethie, and he only gives me lip when it is time to go home. Other than that, he loves to be stroked (not held)
The mini rex are very silly and playful. My mini rex is a delight with his antics.
As for mixing, it doesn't do much to preserve the breed. Responsible breeders tend to stick to one lineage, without crossing.
( However, this may be an accidental litter between a mini-rex and a Nethie - not casting aspersions on the breeder, as I don't know how these little ones came about)
If the rabbits have been handled a lot since they were young, you may have a higher chance of getting one that enjoys being held. However, I don't know that many rabbits that adore being held... rare indeed
As for going to look, don't buy if you don't feel compelled at that moment. It can take a long time to get over the loss of a pet. It is OK to take it slow
Enjoy your visit!