I've had a go at making my own reed diffusers in the past using rattan sticks, a carrier oil (I used almond but I think even baby oil works) and essential oils.
I don't find the scent lasts or is even half-decent to begin with.
The other day I bought the Zoflora 'winter edition' and thought I'd chuck some in my reed diffuser with some almond oil and it smells really good and strong! I've only put it in the downstairs loo so far which is a small space, but it's really lasted.
To buy the diffuser bottle in the first place I bought dirt cheap ones from eBay and threw away the contents but kept the bottle.
It's probably no less chemically than the ones from the supermarket but if you like them, this is a cheap alternative I thought I'd share!