First thing to remember: they are mixed breed dogs. They are likely irresponsibly bred, so unless the person is giving them away, walk away. The person is most likely looking to make a quick buck off their dogs' reproductive organs, nothing more, and will have done none of the things responsible breeders do.
Second thing: there is no such thing as hybrid vigor, at least not the way most unethical mix-a-mutt breeders try to sell it. The only health problems mixing breeds can help with fixing is a simple Mendelian double recessive trait that is present in only one of the breeds.
Third thing: if they are trying to place them prior to 8 weeks of age, walk away. Toy dogs should stay with their mama a bare minimum of 8 weeks, preferably 10-12 weeks
As for that particular mix, they'll probably be energetic and vocal. You'll probably have a long, drawn out house training process. It will shed, and it will need regular grooming. It may end up being anywhere between 5 and 25 pounds.
My bottom line recommendation is don't buy purposely bred mutts. If you want a mutt, go to an animal shelter and adopt one. I'm not saying that every breeder that breeds purebred dogs is responsible, but rather that virtually no mix-a-mutt breeder is responsible. Don't perpetuate their irresponsibility by paying them for it.