I have used Milner before without problems and are very helpfull indeed but this has only been for non critical parts such as front bumper fog lamp units poly bushes etc.
Ideally I like to use Toyota parts certainally for service and mechanical items, cant beat the quaility of OEM, however I have purchased other branded items such as Koyo bearings, these do work out cheaper from a bearing factors than through Toyota, light bulbs, oil & tyres all come from other sources then OEM.
Guess it depends on what you intend to do with the vehicle mines a keeper and I do around 25K a year so I will get the benifit and peace of mind fitting OEM parts, if I was planning to sell then it maybe a trade off on what to fit.