The carts were designed by LAME's, for LAME's and IAW the relevant standards, i.e. colour coding etc.
Extensive consultation was carried out across the network with involvement of both trades.
No they weren't the cheapest or easiest option. They took a hell of a lot of frigging around to get right.
The cheapest and easiest would have been an off the shelf product which didn't meet our requirements so far as ease of use, safety and maintenance.
The carts are coloured coded differently.
The bottles are still grey for nitro, black for oxy.
The fittings are still different between carts.
The only possible deficiency may have been in the implementation and training stage in Mel, but that is purely speculation.
I hate to say it, but it could have just been a monumental brain explosion.