I've heard very good things about that device. I'm currently using the Heltec MeshPocket 10,000 mAh because it is possible to use it as a backup battery for my phone, but I don't use it for that purpose. I dedicate that entire massive battery to meshtastic, and it lasts forever and ever and ever.
I did a full-out drain test on it from 100% to 0% when I got it and I managed to pull over 50 days worth on a single charge.
About the only thing they could possibly do better with it would be to replace the front display with a solar panel and then that would be absolutely epic.