external wastegates its widely agreed are not really needed untill you are over the 500-600bhp thresh hold but some people including myself use them for less as its there if you hike the power up in the future and some people just want one, again myself included lol but i am aiming for around the 500bhp mark anyway to start,

i think the tial 44mm v band is a very popular one to go for and i believe is good for approx 700bhp so more than enough for most people, i have bought one of these and will use it along with a set of air injectors so hopefully will have very accurate boost control, i think the main advantage although i am no expert is using this method (along with air injectors you get no wastegate creep like you can on an internally gate turbo.

The cons of these are only really the cost involved, the wastegates are approx £350 and the 2wd manifold piece modded is approx £180 then obviously you need the turbo to suit etc,
i have asked alot of people about making up my own 2wd manifold trouser piece for external gate just like the reyland item but its not easy to weld to cast etc and just isnt worth the hassle.

Best and cheapest place for the 2wd trouser piece modified for external gate is SCS and cr turbo's for the tial wastegate

hope that helps mate