Nice!
I like deeper containers, also... found some 16 oz cups that are a little taller/narrower than the usual plastic "party" cups (plus they're translucent, like the solo cups)... and for 36 cell trays, I always go with the "deep" 606 inserts.
I've been using half gallon milk jugs for winter sowing for years, and for that purpose I usually cut them halfway up... but last spring I used a few for shrub cuttings in early spring, cutting the jug so I could put a good 8 inches of soil in the bottom part (for winter sowing seeds, I usually use just 4 inches of potting mix). That worked so well, I'll be saving more half gallon jugs to use that way. (The half gallon ones are shaped so that they have taller straight sides than gallon milk jugs... I basically cut the jugs about where the handle starts, and I don't cut all the way through so that the handle forms a "hinge" between the upper and lower parts of the jug.)
I also rooted a few cuttings in the sturdy cardboard cylinders that coffee beans come in... they're maybe 4 inches across and deeper/taller than a gallon nursery pot.
I agree that these tubes would be great for rooting a bunch of coleus cuttings or starting seeds... you could get a whole lot of plants going in a little bit of space, without resorting to those shallow 72 count trays!
good tip on bottom watering with these tubes, too.
Thanks!!