Hi Chris,
I don't have a Grip bag, though I believe them to be a quality product. I was (presumably) in the same boat as you and did not want to drop that kind of coin on a backpack bag. Once I started playing year round, and traveling to different areas to play, I wanted a bag that provided more storage space in one area. I chose the Flak bag for this reason.
During the winter, the consolidated storage compartment is nice because it could be in the 30s when you start an early round and in the high 50s by the time you finish in the Mid-west. The Flak has enough room up top for a heavy duty hoodie, gloves, and hat, not to mention the regular stuff (wallet, keys, phone, protein bars, bag tags, scorecard, pencil, etc.)
During the summer, it is nice to have that area for bug spray, extra water (or beers) and additional snacks, etc. Overall, I feel the Flak bag is an extremely well thought out design and would certainly buy another one if anything were to happen to mine. I also believe the construction is as good, or better than any other bag on the market. Hope this helps.