Why do you need this and a bms? the bms is supposed to balance as well?

Most BMS will only balance while the batteries are charging. The active balancer works all the time. It takes current from a battery with high voltage and sends it to a battery with lower voltage.

can the 20s also be used for a 14s and 16s battery and Lifepo4 and LI

I cannot say for sure-- but I wouldn't think so. The unit comes with the number of leads to match the cells and I don't believe it would function correctly without the same number of battery cells connected.

Will this balancer work without a BMS?

Yes it will. You can actively monitor the state of your battery via blue tooth app and it works quite efficiently. Good for older out of balance battery packs.

Why does daly balancer show diferent voltage on the app from my original bms? Some times in 30 mV diference

Probably the accuracy of the voltage reading. These are not "industrial grade" instruments. they are consumer level. A 30mV difference is not too big and nothing to be concerned over.

Color Name	スマートアクティブバランサー。
Batteries Included	No
Batteries Required	No
Brand	DALY
Manufacturer	Dongguan Daly Electronics Co., Ltd
Size	4S
Product Dimensions	5.99 x 3.51 x 1.78 cm; 132 g

Daly バッテリーイコライザー 4S 1A Bluetoothアプリとワイヤーリード、リチウムバッテリー対応アクティブバランサー付き 定格3.7V 3.2V 2.2V

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Daly バッテリーイコライザー 4S 1A Bluetoothアプリとワイヤーリード、リチウムバッテリー対応アクティブバランサー付き定格3.7V 3.2V 2.2V