Maccy is built for speed: open it with a shortcut, type to search, press Enter. You can pin a few items to keep them at the top.
Clipster goes further on organization: Pins are named boards that group the Clips you reuse (code, prompts, addresses, canned replies), with previews for text, links, images and files. On iPhone, the Clipster keyboard pastes any Clip inside any app.
And let's not pretend otherwise: on the interface, the two aren't in the same league. Maccy is a list in your menu bar, and that's exactly what it sets out to be. Clipster is a real app: cards with previews, code shown with syntax highlighting, the icon of the app each Clip came from, Pins with their own icons, drag and drop straight into another app, and a light or dark theme. Both paste in a keystroke; only one of them is a pleasure to look at while you do it.