I have a friend who skied with Trekkers in the BC for a season (about 25 days). They were a hassle but were better than not going.
Mudfoot's observations are very accurate. I would also add that they take significantly longer to transition between skinning/skiing. If you have Trekkers and your friends are in tele or AT gear... pray for patient friends. That said, they worked fine and once you accepted the drag of boots not made for walking and the extra weight they were OK.
Trekkers really shine when you go through the gates at a resort. Toss a pair in your backpack with some skins... then if you end up someplace where there isn't a readily available lift you can still get back to where you need to be.
I have a pair for friends, too, who don't have a real BC setup but who want to join me on BC days. Trekkers, some old skins, a spare beacon/shovel/probe put them in pretty good shape to head up the hill with me.