Pete,
I can appreciate that a bigger size might be an advantage in certain circumstances but we are talking here about raising seedlings so there is a limit to how big you should go, too big a pot/module could lead to problems with overwatering etc.
The question really is, do these soil blocks offer a significant improvement in seedling quality over conventional module trays to warrant the extra work required to use them. I think not.
Peter,
That type of pot has been around for years in the shape of aquatic pots. I have been using these for bulb planting in the herbaceous borders for years now. What that article shows is just a different style of the aquatic pot.I find them useful in that I can plant and later lift clumps of bulbs for storing over winter and as they are in these pots no bulbs get left behind to surprise me next summer.
I would also add that I would think that that particular style shown in the article would cause significant root disturbance if you were potting on from one size to a bigger size,
Don.