They are definitely good for all public land for the season and unit, hence the phrase "Unit Wide".
The reason the current voucher system is under review was touched upon in one of the earlier replies, but this is only the tip of the iceberg.
One of the biggest issues is that the Landowner Voucher is issued to a "landowner" who in turn sells the voucher for use on public land vs private land.
There have been times (I've seen it here) where unsuspecting hunters purchase a Landowner Voucher for a unit that has leftover tags. Therefore, they spent money for a NR license and even more money for the voucher when all they had to do was purchase the NR leftover tag. Some hunters may even think they have the opportunity to hunt private land because they're purchasing a Landowner Voucher but this is not necessarily the case.
On the other hand, there are hunts available from private parties (guides/outfitters/landowners)that include the Landowner Voucher AND the opportunity to hunt their private land.
Also, it could be possible that a voucher is a hunter's best option to get in the woods that year due to any number of unforseen reasons. For example, a hunter could spend a year planning a hunt to find out in July that he didn't draw but he still would like to hunt.
I'm not jumping either way on this, but as with anything, BUYER BEWARE...
