Why bother with all that extra valve crap? Corny kegs are perfect for a secondary. They can hold a crapload of pressure (over 100 psi) so if you do still have fermentation building up some CO2, if you pull the pressure relief valve at least once a day you'll be fine.
That's all I do for secondary fermentation. Corny kegs. When it comes time to rack, you just put a jumper on from one corny to another and the beer never touches air. Its perfect.
Safer than lugging around big glass carboys too.
There are many advantages doing secondary and tertiary in cornys.
MAJOR THUMBS UP.