IMO the white cutting mats that are not self healing are not that good when using a rotary cutter because they wear out the blades a lot faster then the self healing mats. My best guess is that while cutting your fabric, you are also cutting into the plastic which will soon have grooves in it which is why they need to be replaced so often and that also puts more ware on the rotary blades. Since I found this out, I have not had to replace my rotary as often and that in itself has save tons of money.
Now if you are talking about a self healing mat of that size by all means YES it is the best thing in the sewing world, to have a large mat that you can leave on the table at all times to cut on. I have a large white mat, the first one I bought still on my table, but I leave it there for protection only. If I want to rotary cut anything, I just place a good self healing mat on top and do my cutting.
SO to answer your question, if it's not a self healing mat, take it back, use the money to towards getting a good self healing one. Cost may be more but the saving you get on your rotary blades will end up being worth the extra spent.