nano tanks

So I've decided to break down my 6 gallon which housed my scarlet badis before I had to euthanise him, mainly because I don't know exactly what caused him to go downhill and want to give the tank a good clean just in case. I'm going to put new inert substrate in, throw away the decor (ornament)...

I've noticed detritus worms in my nano planted tank before and have even tried to get rid of them but I saw online how they're potentially a food source and recently I got a first hand look at my bumblebee goby feeding on one.

Recently I have noticed out of town retail parks selling a few liters goldfish bowls without filters or anything else for a few pounds . So my question is are they suitable for keeping anything in and if so what ?