The abacus my daughter is using in the Mental Math post is called a Japanese Soroban. With this abacus there’s only 1 bead above the bar and 4 below. It’s very useful for mental math.

The Chinese abacus has 2 beads above and 5 below. I don’t have any experience with the Chinese abacus so I can’t comment on it.

I have 2 Japanese Soroban abacus’, so if you’re looking to buy one of those I can give you my tips that I would look for if I was buying another one. I have one that has a reset button, I find that a handy feature. Also, I have one where I wish there was a little more space between the beads and the bar, it would make it easier to clearly see if the bead was being counted or not. Also, for adults anyways, I find it important for the beads not to be too small or at least a smidge of space between each column of beads. The one I have with smaller beads has no space between each column of beads and with my adult hands it’s a little too confined. My other one that has I would say about 2 mm of space between each column I would say is perfect in that regards. The last thing I would be looking for would be how the beads glide. I guess that’s hard to tell if you’re buying online. Ideally they would glide easy but still have a bit of resistance for better control. Some pretty multiple colors would be nice but not critical.

The abacus that has 10 rows with 10 beads each is not really for mental math but can be a useful tool in general for math. I have one I got cheap at IKEA (not sure if you have an IKEA where you live). In regards to abacus apps for Android, I have no idea sorry, I don’t use Android.