Any protection is better than no protection. No questions that G Technic C5 is a class act. However for something less expensive & less permanent have a look at Autoglym Alloy Wheel Sealant, easy to apply but it would need regular applications when compared to other sealants.
Some of the wheel sealants like Poor Boys, or Chemical Guys Wheel Guard, these would be superior, have a look on detailingworld.co.uk for reviews. Have a look at the sponsors website too for options:
http://www.detailingshed.com/15-wheels-tyres

I have huge time for the Car Pro range in general so I would like to give this a go:

http://www.detailingshed.com/plastic-trim/226-car-pro-dlux-kit.html

It is pricey but like GTechniq it is a lifelong coating.