The standard Rotax bottle is indeed plastic, but it's not held in place with "ears". Anyway, I'm not saying that mounting method is wrong, just that it's something to be keeping an eye on.
I guess the lanyard on the cap will stop you misplacing the cap, but how often will you really be taking that cap off?
I'm curious what you are using for the connecting hose; can't see it in the pic. I recently replaced mine with a clear, high-temp silicone hose, so I can see that there's always fluid in the hose itself.
Pretty sure the lanyard is to make sure if the cap comes loose it doesn't go through the prop. I thought that was an excellent idea. I have to get myself back into the pusher engine mentality again, where anything that can come loose will eventually go through the prop.