I have to agree with you. I rolled my own Linux router solutions for years but made the switch to Sonicwall two years ago. I deploy TZ-180s at all customer locations and set up a VPN tunnel to my NSA-240 where there virtualized server are located. Can this be done with Linux? Sure but buying the parts to build something the size of a TZ series costs nearly what it costs to purchase the TZ-180 (without the extended service agreement). I have enough 180s deployed that I keep a couple in stock as hot spares rather than spending the $ on the service agreements.
The best part is that clients are able to access their servers from home/on the road/etc with NetExender to a SRA Virtual Appliance. I think this is where Sonicwall really shines. The ability to install the NetExtender from a web portal with a couple of clicks saves me many hours of trying to walk a client through how to configure a vpn connection on their home computer. In addition the SRA supports Windows, OS X, Linux and iOS devices and the clients are all no charge. It's simple to configure a custom portal for each customer including bookmarks to file shares, rdp sessions, etc. And the best part is that the authentication for each portal is easily pointed the the customers DC's, a thing that Has always been a problem for me with Linux routers.
While I was not a fan of Sonicwall in the past I believe today they really provide a nice range of products at a reasonable price point.