Can of worms, opened.
I've been wondering how to get a healthy male from a Strain only available in Feminized.
Quick answer is, it can't be done. You can't cross only female plants and end up with a male one.
In practice, you can "reverse" a female plant to create pollen, and use that to pollinate another female plant (or even the same one), thereby avoiding the need for a true male. This is how "feminized" ceeds are created.
Also, in practice, most strains available as "female only" are hybridized, and if you were to cross them with themselves (or even a male of the same line) you wouldn't end up with offspring that looked exactly like the parent, but instead a variety of phenotypes.
Feminized seeds arent good for breeding.
Don't think the original question was asking about "breeding"; it was asking about male plants.
To be clear, there is a difference between BREEDING (ie creating NEW lines by crossing others and doing selection) and just making ceeds. Its necessary to create ceeds to do breeding, but its certainly not sufficient. IE, in my opinion, just crossing two plants to make beans isn't really "breeding", its just ceed-making, and there is a difference.
To address the can of worms, the conventional wisdom amongst breeders is that you don't breed with feminized ceeds. I've heard any number of breeders SAY this, but with one exception, I've never heard anyone give any kind of scientific/genetic/or other plausible explanation what difference it makes, or why you shouldn't.
From my perspective, there is no fundamental/genetic/chromosomal difference between a female plant that has two female parents vs one that has a male and a female parent. I don't know what difference this makes, and I chalk up this to just breeder "superstition".
The exception is that Ed Rosenthal (expert grower, author, and former cultivation editor of High Times magazine) has said that *IF* you start using feminized beans, and do selections for plants that are easily feminized you're going to impart a tendency for hermaphroditism to the offspring. That actually does make sense, but it implies that you're using feminization over multiple generations in your selection, not just one. In other words, you're doing ALL your breeding using JUST female plants. In this case, I would agree with him at least in principle, though in practice, a. Nobody does this, and b. Even if you did, I think if you were careful to look for and cull out hermies, it might not matter.
The fact is, a significant plurality (if not absolute majority) of small growers are starting with feminized ceeds. Its to the point where several companies offer nothing BUT feminized ceeds, and a few of the breeders that said they weren't going to offer any have relented to market pressure and started doing so anyway.
But the point is, there is nothing intrinsically wrong with fem ceeds from a growing standpoint, and you can get excellent plants this way.