On the left is what the Goodyear Allegra tire now mounted on the driver-front looks like, along with the new spare placed beside it.  (The odometer is currently at 51,762 miles.)  It is the type of alternate tire I selected to put on my Prius when the original Bridgestone Potenza tires wore out.

The tire is not XL (extra load) rated, so additional PSI was needed to compensate for the heavier-than-average weight of the hybrid system.  I selected a tire-pressure of:  42 PSI front  &  40 PSI back

After 18,000 miles of driving with these alternate tires, I had observed how well they handled the weight, how nicely they gripped the road, and how evenly the rubber was wearing.  So I increased the tire-pressure to:  44 PSI front  &  42 PSI back

On the right is the tire now mounted on the passenger-front and the spare.  If you look very closely, you can see the "wear bars" between the vertical tread pattern.  They indicate that there is quite a bit of rubber remaining, much more then the original tires had at this point.  So I can confidently say that these tires will last quite a bit longer than the 31,000 miles than my Potenza tires did.

The tire is not LRR (Low Rolling Resistance), so MPG isn't quite as good as it could be with at the same tire-pressure.  However, I had to increase it from the original 38/37 PSI that I used anyway to compensate for the weight.  That fact, along with the fact that the Prius is much more broken-in (aged) now and that I've switched to synthetic oil, has pretty much cancelled out any MPG loss.

In short, these tires have proven to be an excellent choice.