Re: Bored so I built this
Our club has several designs of benches on the line, some quite old.
Massive legs like those in the OP work well until the wood dries out and the fasteners loosen. The addition of triangular plywood gussets will prevent the inevitable wobble.
Bench tops also dry and shrink. When the tops are made of planks, gaps appear which become traps for .22LR casings. Make the tops with whatever you choose, but cover those tops with plywood.
It can be annoying to have to get up and pick up something which has rolled off the bench and onto the ground. Generally, if such things happen once, they happen plenty. Wrapping the edge of the bench top with a 1x2 molding that extends upward above the top's edge by about 1/8" can forestall a significant number of cussin' sessions.
Sharp corners are bone bangers. I hates 'em, and I cut corners with 45 degree breaks wherever possible.
Attached seats... Some like 'em, some don't. I like 'em 'cause they don't wander off, and I know that my seating position is consistent to the degree that seat position is not an issue.
My bench design uses a plywood top that's square with one corner cut off. The cutoff is mounted lower as the seat. The bench is ambidextrous. Turn it with the seat on one side, it's a righty, rotate it 90 degrees and it's a lefty.
Finally, before you start using a bench, check underneath. Ticks and wasps like to hide under them.
This image shows myself and a few friends on the line at our Club after an FV200 match some time back. The bench in question is in the far right foreground. Not especially well visible, the far bench is identical, and another is off to the left, out of frame. Although only part of the bench shows, enough is there to illustrate the points I suggest.
These benches are not in complete conformance with all of the above suggestions, but they are left out year round and are going on a decade old. They are still completely as rigid as the day they were built. The design allows three square tops, 32" on an edge, to be built from a single sheet of ply, with no waste. Future benches will have less 2x4, more plywood, and bigger tops.
Greg