Nitecore F4 vs. Xtar PB2S

I thought I was trying to decide between these two chargers, but after more research, there’s a lot not to like about both of them. Just wondering if my concerns maybe aren’t very good concerns, or if my information isn’t good.

Nitecore F4:
-inefficient charging. Uses 2A to charge left most bay, then slowly drops off then picks back up to 2A for the next bay. I’d rather slow charge all cells than fast charge one cell.
+better LVP level at 2.9V when in power bank mode.

Xtar PB2S
-during power bank usage, LVP is very high (3.3V), so much of the battery capacity isn’t used.

My other usecase is to power a raspberry pi with these. Has anyone tried to do this before? Does the output voltage drop off for a second when when the power bank switches from one 18650 bay to another bay?