IMO... if you're peripherals have a low battery warning that you depend on, these might not trip them (I don't know).
Another potential downside, is that you will always have to use the USB cables to charge. I don't think you can use a charging dock for these.
I've been contemplating on getting some myself. I might try them out in the future. My main worry is that I might be hesitant to use a Li-ion rechargeable in a AA/AAA device that wasn't designed for it in case of catastrophic event/failure... especially if they are used in series.
Keeppower makes Li-ion 14500 with micro usb. If you type in something like "14500 usb" into google, quite a few results show up, most 3,7v, also one or two NiMHs. If those are any good IDK, namebrands like Keeppower, Nitecore, Nextorch, Klarus should be fine. Fenix seems to make a 1,5v one. Are all of those unsuitable?
I have few Keeppower 1.5v AA 2260mAh. They are USB charged Li-ion batteries with regulated constant 1.5V output.
Works well in my SL Protac90 with constant high output. My Olight i5T has timed stepdown so it won't keep on constant high.
I've been looking at this type of cell. Biggest con is they're all about $5 each! The EBL with USB ports were temp sold out so I ordered the other kind that has a special 4 or 8-slot charger. I don't need to USB charge them "in the field" so it's really sixes, as far as I can tell, between the two types.
I want them for some LED candles that run off 2xAA and get too dim when the batteries (alk or NiMH) are at about 70% charge. I have a radio that doesn't like <1.4V, but I think the electronics in these batteries put out a lot of RF hash. Might work on FM, still.