good question. What I care about, of course, is maximum efficiency in
the whole process. I can now seed a tray in a minute or so (seed being
cheap). I am finding, however, that I spend too much time replanting
things that have bolted or went into transplant shock, in part because
sometimes I use the 288 cells trays, which have little soil attached to
the rootlets. So I am going to go with the larger blocks which is
potentially a lot more work. The things that shock/bolt most often are
cardoon, cukes (and next year I expect watermelons too), peppers, savoy
cabbage, dandelion, and a type of green chicory. Brassicas in general
are tricky, wait too long and they become rootbound, go out too early
and they get shocked. I don't have the time to ferry trays in and out
to harden them (I just time my plantings according to the weather, if
it is sunny I do other yard work, if it is overcast I plant), so I am
hoping that giving them a bigger pot/block will please them enough.

Now the pizza cutter won't work (it is not deep enough, and it will cut
the bottom of the tray, and then you have a mess). I have experimented
with half Scottex paper roll cores for the cucumbers (they are 5''
deep, the cukes won't shock when transplanted), and that looks good.
One possible option is to use those cardboard grids inside wine boxes
(those that keep bottles separated). In fact, if you cut one with a
large paper cutter you will get three such things. But I suspect that
roots will happily grow into the moist cardboard. That is why I wanted
to hear about first hand experience with the blockers. Things like,
when you pick up the block, how do you do it, does it fall apart, etc.