Surprisingly it's not true. Bottom fill tanks where you can unscrew the deck and fill the tank are very easy to fill with one hand having an atomizer stand like this:
You just put the tank upside-down into the stand and unscrew the base.
My previous post said my first suggestion. But the best bottom fill device I have that you can easily find, is the
Goblin mini. The only thing I don't like about it, is it uses a non-standard drip tip, and relies on a drip tip adapter to fit standard 510 drip tips. It is, however, one of my best flavor tanks. I haven't used mine since I got the Smok twister, but I plan on getting those back into use tonight or tomorrow. The refill screw is flat head, which might pose a problem for single handed unscrewing, but if you can find a phillips head that fits, I'm sure it would make it a lot easier. I also found that the glass drip tips break if dropped, so If you do decide to use the glass drip tips, order
extras just in case. The airflow is fairly open, which may not be suited for you, and I find even in the fully closed position, the airflow barely borders the high side of MTL hits.
Just thought I'd give that a mention.