I use a few different breeder boxes, and while none of them are perfect, they seem to do the job for me. I don't have any idea what models or brands they are, besides one - the Aqua One Mini Float. I bought it for endlers and shrimp, and I doubt it would work for guppies, mollies or any other larger livebearers, since it is (as the name would suggest) pretty small. It's hard plastic, which I like (for usability), the suction cups kind-of suck, although it does have two compartments on either side that hold air, so it won't sink if the suction cups come off. It's a great size for my 5 gallon tank. My problem is that the gaps are too large for shrimplets. I think there should be some alternative option that has a very fine mesh (like in a shrimp net) that can be attached over the areas that have water-flow holes. It also comes with a removable divider for fry seperation. I do prefer breeder boxes with a divider option.
I also have 2 of those rather common large mesh ones, that pack really small and have a net that goes over the hollow-cube structure. One has 2 dividers (so you can subdivide it into 2, and have a baby-catcher underneath still) which I found very useful when I was breeding lines with 1-2 males and 2 females, as the females would drop their fry around the same time. So I think the metacube idea is a really good one. There are a couple reasons I prefer hard plastic (with a fine mesh attachment possibly) over mesh with plastic scaffolding (like this) - firstly, the plastic ones are easier to move when you remove the fry. I have on multiple occasions accidentally left a fry in the mesh one without realising. Luckily I noticed in time, and I haven't had any deaths from that. Secondly, there are slight gaps between the mesh and the scaffolding, and the fry have a tendency to get stuck in those gaps. If I don't notice, there's a fair chance I could lose some of those fry. I also have problems with the mesh ones getting algae on them. If the hard plastic gets algae, I can easily rub/scrape it off. The mesh just does not let go of algae though, and it can be a bit of an eyesore (in addition to how ugly the mesh ones already look). If I try to suck it off with a syphon (just cuz) the fry get sucked into the net and stuck.
I hope that's helpful. I do realise it's a massive mess of text. To sum it up, the things that are important to me as a shrimp, endler and guppy breeder are the following:
Clear, hard plastic box
Divider option
Safe for baby shrimp
Has a possibility to use multiple beside eachother - possibly interlock
GOOD suction cups (like Eheim ones)
Smaller size
Works with and without a lid
No places for fry to get stuck.
Cheers, Crabby.