I've shot lam birch for years.
Durable, heavy, and for the most part consistent when purchased from high end retailers (have had a few 'culls' that ended up as tomato stakes).
I don't shoot a bow under 65#'s, so for me they are one of the few easily available wood arrows that give me the weight and spine i need. Needless to say, i don't have a trajectory issue like those shooting lighter rigs will have.
I have found the key is to do two rounds of straightening by hand BEFORE any finishing work. Use a hair dryer or heat gun, but don't heat them too much (too hot to touch), or you run the risk of damaging them.
Straighten and roll on flat surface. Use a bottle for burnishing as well. Once they are straight, bundle them up tightly and let them sit for a week. Repeat this again after a week.
Then cut/taper and finish. Be sure that ALL exposed wood is sealed. That is the key with lam birch. They will stay incredibly straight if they are completely sealed. I like spar varnish, about four coats with light steel wool in between.
I have some lam shafts that are still perfectly straight seven or eight years later, after multiple trips in all kinds of weather.