Aspen is a swedish fuel company specializing in cleaner fuel for forestry.
I run my 1983 Yamaha XT 400 on alkylate petrol (Aspen 4)
It took a couple of oil and filter changes the first 10000km, but it cleaned out all gunk in my engine.
I would only use it in an older carb bike with new seals though, since it most likely would void your warranty on a new bike(ask your manufacturer).
The thing is, you can't go back and forth between it and regular fuel unless you want to seize your engine.
I pay around £1.50 per liter when buying 200 liter drums (in sweden), but since it burns cleaner and wastes less fuel i end up paying about the same as regular petrol(with a bit more effort though).
But in return I pass the MOT emissions tests with flying colours, barely any smell when riding or in the garage, long storage capacity (left it for 3 years in cold storage and it started instantly)