Depends what you trying to achieve.
Personally, I don't use, or like mini nucs. The smallest unit I use is a three frame medium box. Most breeding boxes are three and five frame deeps.
Why you ask? .....Well I'm happy to explain!
Ever get a bad queen? A drone layer, or one with a crappy pattern? I have. And many times it goes bad to the weak management of the queen producer. Please note that queen producer, and queen breeder, is two different things.
The queen industry is notorious for the "see an egg, pull the queen" technique of queen production. There is no way for anyone to truly evaluate a queens performance in a mini or baby nuc. Some will suggest they move the queen to larger units for evaluation which is pure B.S. most of the time. Rationalization is just lies for many.
Mini nucs confine the queen on such a small amount of comb that she can easily go back and forth many times in one day and have a pattern that looks fantastic. And any good queen breeder knows that 10-20% of all queens will be duds. So how are you supposed to cull out the bad queens if you have no way of actually seeing what the queen is doing from the inside of a mini nuc? This is why bad queens are passed along to the consumer way more often that should be.
I like using full frames. I can pull them in the spring from strong hives, and combine them back in late summer into bigger units to overwinter. I have no wasted comb or dead mni-nucs at the end of the summer.
Mini-nucs are good for the mass production queen producer. But bad for the purchasing beekeeper.
For the backyard beekeeper, I find the purchase and cost of the mini nucs a real waste.
5 frame (or three frame) nucs are much more flexible in application and can be use for many uses. (Swarm traps, found swarm cells, etc.) mini nucs are use for one thing and one thing only.
If your only raising one or two queens, why buy extra equipment? Any box will do. Production is still production. So why not have bees drawing wax and filling comb in frames you can always use?
Mini nucs push the envelope of what is needed to feed, take care, and produce quality queens. I'm glad my operation is not based on that outline for success.