In the meantime, I have tested this Active Balancer in various configurations. It turned out to do an excellent job. One drawback is, that you must turn it off below some 3,35 V cell voltage. Otherwise it will execute Bottom Level Balancing, when you discharge your cells below some 3,1 V. This will bring your cells out of balance, which shows at the next end of charge event. If you use a BMV700 Monitor in your system, you can use the relay output to automatically control the balancer. Switch the balancer on at 13,48 V and turn it off at 13,40 V.
The big advantage is, that your cells will be perfectly balanced at low charge voltages, e.g. 13,9 V. Low voltage means less stress to your cells.
Cheers Hans