Randy - I really didn't round off the corners, other than sanding them a little bit more, than the rest of the block prior to the poly application. I have used them on end without difficulty. The handles make the blocks easier to deal with, easier to see when leaving a campsite so I don't leave them, keep my hands/gloves cleaner and drier and reduces the chance of splinters.
John - These blocks are not used to raise the Titanic. Since I rarely camp during the winter, they are rarely used in sub-freezing temps. The application of the poly was intended to prevent water absorption and make them last a bit longer. The main purpose is for use as "stabilizers", fine tuning the level of the camper and as Steve says to save time, lessen the use of power to the jacks, and reduce the risk of a bent jack. If I need to "level" the Oliver to any great extent, I normally use either "legos" or ramps under the tires on the low side. No, I do not use these for winter storage - they are too pretty to be left out all winter ;)
Camp12 - Welcome also! In addition to Steve's comments, I've found that these can be used when my campsite is not very level (think mainly boondocking here) and I need the extra height on the low side - I really don't like extending the jacks to the limit if I can help it mainly due to the torque that might be applied to them.