One of those links for one that says it supports different voltage batteries also claims connecting two 60A max discharge capable batteries with this gives you a 120A capable system. Nothing could be further from the truth.
Clarification for readers that don't know electrical principles:
Paralleling two batteries does, in principle, allow for providing twice as much current (A).
In reality, you would never want to use a system capable of higher current draw than the lowest-current-delivery-capable battery in the system, because if any of the other paralleled batteries fails or disconnects for any reason, you don't want to overload the lower-capability battery(ies).
And, of course, if you have a system with different voltage batteries, they can't both be connected directly in parallel and thus can't both supply current to the system at the same time. Only one of them will supply current at a time, until the higher voltage unit has drained enough to equal the lower voltage unit, and then both will be able to supply current *if* the "blender" device works in a way that allows this.
Some of the combiners / blenders / incorrectly-named-balancers use simple diodes, and those will allow that to happen. However, those by necessity don't allow regen, so you cannot use them on a system that has regen or you can blow up your controller.
Some are "smart" and thus unpredictable (by the user) for how they will work, because they never say how they are designed inside, either electrically or software-wise, and thus we can't know (without testing each possible variation) what is going to happen in any of the many variations of battery states and system current draws or current directions.
But...virtually none of the devices actually say what they are inside, so without testing of all the possible situations, you won't know how the one you buy performs in any of those situations, or what it will do to your batteries.
In general, I would not recommend using any form of prebuilt device like this, unless you know *for sure* how it works, and what it will do in all the situations you will be using it in.
It is much more predictable to simply directly connect your batteries' discharge ports in parallel, *after* ensuring you have charged them both to the same voltage.
If the batteries are different full-charge voltages, you will only ever be able to charge them to the lowest-voltage-unit's full voltage.
If the batteries all have common-port BMSes, meaning that they charge and discharge thru the same pads on the BMS, then youc an leave them connected while charging.
If they have separate-port BMSes, or you don't know *for sure* what kind they have, you must disconnect them from each other while charging, and only reconnect after charging is complete and charger is disconnected.
Don't leave the charge ports connected to each other, when not charging, either.
Reasons for the above are clarified in detail in other posts about this sort of thing around the forum.
