Its an inexpensive way and its an iSUP so should be able to take some beatings. You will upgrade very fast, trust me. I bet you own more then 2 in the next year. So that $500 one can be for guest, or kids. The paddles that come with those cheap boards are complete garbage so spend the money on a good fiberglass if you are using in rivers or carbon if you only use for flat water. Carbon does not do well with impacts with rocks, tress, etc. I use a Werner for the river.
I would look for a used one though, they will be of a better quality and with inflatables that only issues I see after years of use is if they pack it up the wrong way. The creases can start to wear the PVC and create holes.
My buddy has two cheap boards he got for $600 a piece and he uses it on river, lakes, etc.
How thick is the costco one? If its 4" it may be to thin for bigger paddlers. 6" are way stiffer too and better for river running and multiple people on lakes. What are you using it for?