There are different flight schools that do this.
I am not refering to any of them but trying to clarify that all the saving that may bring is just around 100$ per student on an entire training...
Not much when you consider that they rip you off a few dozen K-bucks on your entire training!!
About JET A1 aircraft, the cost of JET A1 is significantly lower but maintenance is more expensive.
The Thielert engines for instance, you need to replace them completely every 2000 hours. Their reliability is also not very good.
Also, many schools are buying DA-42 which are very expensive aircraft, about half a million bucks at list price. The fuel costs are significantly reduced but until you can turn that investment into profit, it'll take quite some time.
The DA-42 is a state-of-the-art aircraft but me and my company slightly disagree with its philosophy, certainly when you think that it's the students who will need to pay for this high cost investment.
After all, training shouldn't be a matter of luxury...
But then again you can also start questionnig about schools that prohibite any training when you have more than 6kt X-wind...