Cool device but doesn't look very pocketable.

Anything's pocketable with sufficiently large pockets ;-)

The Psion would fit well into a coat or jacket pocket, or cargo pants/shorts, and easily fit into a satchel or messenger bag.

The Psion S3 dimensions are 165 mm x 85 mm x 22 mm (6.50 in x 3.35 in x 0.87 in). Contrast the iPhone 15 at 147.6 mm x 71.6 mm x 7.8mm (5.81" x 2.82" x 0.31"), and the iPhone 15+ at 160.9 mm x 77.8 mm x 7.8 mm (6.33" x 3.06" x 0.31"). Other than thickness, these are pretty comparable.

What it offers most specifically, however, is a useful and usable set of capabilities, in both hardware and software: full keyboard, email, calendar, Web, word processing, spreadsheet, contacts.

I've known journalists who've used it as their mobile platform for gathering and filing news stories, which also means it passes the "professional use" test.

Dimensions from <https://en.wikipedia.org/wiki/Psion_Series_3> and <https://www.apple.com/iphone-15/specs/>.