Homebrew, works out about £10 /litre, works fine.
As per thread on MTBR covering it, basically 10-15% screenwash (proplylene / ethylene glycol antifreeze), 20-25% water and the rest art shop latex. The more latex in the mix the faster it seals bigger holes but the less time it lasts before making latex coral in the tyre (as Stans does). Add the latex to the screenwash not the other way round to avoid coagulation. Slime or glitter is said to seal small cuts faster. I don’t use it, I’ve flinted a few tyres and got a white spray to add insult to tyre injury but not bothered with slime/glitter yet since it seals thorns etc without loss of pressure.