I don't think the liquid in them is anything special but the design seems better than my open dishes of liquid so hopefully this works.
Commercial fruit fly bait is just a powdered version of the usual stuff you'd mix up; I refill fruit fly traps with white wine+dish soap all the time and have no problems. The commercial baits I've seen (that come free with traps) are usually attractants, sometimes surfactants, and the only unusual thing is sometimes they have a meat scent as well as the rotting fruit scent.
You can DIY something similar by cutting off the top of a bottle of water and inverting it over the bottom part.
In my experience, DIY fruit fly traps work just as well as purchased ones and are easy to make and no guilt for throwing away.
There are only two potential drawbacks to DIY fruit fly traps: sometimes they look shitty enough to make you feel bad about your kitchen.
More importantly: if the DIY fly trap is big, kludged together and made of light materials, you may end up with dead fly cocktail dried all over your counter because it turns out your cat thinks that "don't get on the counter" only applies when the human is awake. Or you bump it yourself, or the people you live with don't give enough of a crap. It's easy to knock over the inverted-bottle trap, and now you have to clean up a gross mess while you're already annoyed at having an infestation.
If you don't care for the plastic reusable traps, or you want to get it out of the danger zone on the counter, I really like the old-fashioned glass fruit fly traps:
They have a funnel-hole in the bottom for the flies to fly into, and little bumps on the bottom so you can set it on a flat surface, but I've had them work even better in the window where the light is also an enticement. You can also hang them right next to a hanging plant, if the plant is part of the problem.