I used to fill this up whenever I had a money off fuel voucher from superstores, I would then fill my motorbike up so that I wouldn't have to drop into a forecourt when kitted up.
If putting this in the boot of the car, you will need to secure it upright or it will fall straight over, although it is leak proof, it isn't ideal to have it sliding around with a risk of catching and pulling open. I had mine held up with bungee cords, but you can buy cages for these.
To fill up my bike I used a nozzle from another Jerry can and a funnel that had a mesh filter as I noted that some buyers had experienced paint flakes in the fuel. I can't say I ever noticed any when filling up, but didn't take any chances. However it has been empty for almost a year now and I will have to check to see if that is still the case.
The only reason I have stopped using this is because many forecourts will only allow you to fill up a max 10Lt Jerry can. You can probably get away with discreetly filling it up out of eye line of the cashier, but I don't want the embarrassment of having a telling off via the PA system. So I now use a 10Lt can