When do I need such a thing the most?
When I travel far.
When is it least likely to work?
When I travel far.
(Due to different plugs etc).
I fully support the idea of having an 18650 ecosystem, and it works really great for me.
Part of what makes it work really great though, is the individual cells. I don't want a charger I can charge my light with, I want to swap the cells, so I instantly have more power.
I can use the same cells in my Zebralights, to charge my phone (Nitecore F1), I can charge the cells from any USB-port (again the Nitecore F1). Need to tank up in a hurry? Nitecore SC2 will pump 2-3 amps safely into the cells, SC4 on the way.
Wondering if the cell is getting old? MC3000 will tell me if it is.
Got off a stinky habit using vapour, and the same batteries are good there too.
Headlight? Again with the same battery.
So what about travel? The chargers I have that are not USB-based, take a wide voltage range, and use standard cables. Not even adapter is needed, I'll just pick up a proper cable locally. 12V works with (I think) all of 18650 chargers, allowing for car-usage and lead acid backups, even solar.
Now, I do cheat a bit. If I'm comfortable traveling heavy, I'll also bring a 20Ah power bank that'll USB-C recharge (really fast), and I have a 5-port fast USB charger as well. Both are relatively lightweight, and allows me to charge fast, so I don't need extra downtime at hotel for charging etc.
Power banks also allows me to fetch power from airport charging stations, without having to leave my phone there, and without the virus risk.
There are downsides, there are protected and unprotected cells, flat- and button top, and some lights might require one or the other etc, so it's a bit to navigate, but worth it (IMHO!). Also requires careful handling of the cells, to not short them etc, but "battery condoms" makes it less of an effort.
Ordered a few smaller battery packs as well, might be nice enough when I don't want to lug the 20Ah packs.
Sorry for the long writeup. Major points with my setup vs. the fusion:
Lugging larger power solutions is a pain. Check out the size and weight of Anker 2-3000mAh banks and 5000mAh banks, against the fusion. Which would you prefer in your pocket?
If you need wall-charge, IMHO it's very nice to have more than one. A 5-port charger would let you charge phone, 2-4 18650s with Nitecore F1/F2, and two powerbanks. All at the same time, for not much more weight. It also allows for "charge one, use one", and you just have to carry the one.
Swappable cable and 12V options are also very useful.