The RM has the advantage of Gold efficiency and a 10 year warranty. Also as you are more likely to point the PSU fan downwards,the lighting won't make as much of a difference,as opposed to the RAM,fans,motherboard,etc.
Gigabyte has UK based RMA
AFAIK,and there was even a CS chap from Gigabyte who was on OcUK forums:
https://www.overclockers.co.uk/forum...iga-man.78904/
Amazon Warehouse is apparently "different" to the main Amazon website,so not sure how warranty claims go through them. But generally if a product isn't as described its easy to get a refund or maybe some extra money off. However,I have used them too for parts in my build,since you can get some great deals.