Hi Csaba Major
I have recently purchased 2 x A20 Mini units and the A10-RX for my SL-2 and SD 833.
I'm using a generic Sony NP-BX1 battery with the same specs (about 4Hrs run time with record at 10mW ) where it's possible you have the ability to add a small/large battery bank into the A 20 which will increase your run time by ... That of course is not always practical .
I use Lectrosonics SMWB's with Eneloop Pro AA's and have managed to get close to 8 hours out of a unit, so I know the A 20's will take some getting used to. But as long as they make it to lunchtime...
I am running DPA 4060's and 6060's with the A 20's. I know this site isn't a fan of superlatives, so I'll just say that they sound like a wired mic... nice.
The app works well enough with a lot of options, I'm sure there will be improvements though.
The gain control is immediate through the 833 and SL-2.
So far I have no regrets adding 2 x digital Tx's to my kit.
I hope this helps.