How wide of hole is the 18 gauge making? Head width or much wider? I don't have a HF nailer, but my senco has a pretty narrow driver, which also has a dial to set the depth. The driver is barely wider than the head, but 18 gauge holes are pretty visible from what I've seen.
I do have the HF stapler and have been very happy with it, mostly use it for shooting underlayment down or backs on to cabinets. Don't have the pin nailer, but have one on my wish list. I think you've got the right idea for when to use it. The pin doesn't do a lot but hold the piece til the glue sets up and is pretty invisible.
To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault