Metropolitan does have longer gearing than Ruckus. As result, due to tiny engine, the top speed on the Metropolitan is a lot lower than the Ruckus, if we're talking stock form on both. Just not enough oomph to take advantage of the longer gearing and reach higher speeds.
Metropolitan is a little tighter than the Ruckus. I'm 6'1" and could not fit on the Metropolitan without my feet touching the handlebars at turns. No such issues on the Ruckus though. Plus, due to Ruckus naked frame style, I was able to buy a lowered seat frame that also sits farther away from the handlebars, giving me more room.
My advice would be to buy used, stock, and low miles. New ones not worth the premium, upgraded ones are usually plagued with issues from people not being able to tune the carb correctly. But in stock form - a reliable little bugger with plenty of style and smiles per gallon. 100+ MPG is nice too.
Despite being very similar mechanically, they are very different. For example for upgrades: It is possible to give the Metropolitan a "big bore" upgrade at 83cc, while Ruckus only had 58.1cc "Big Bore" option. Both 49cc originally. It's discontinued these days, unless you can find one on forums for big money. And due to being liquid-cooled the big bore upgrade isn't done with a simple afternoon head&piston swap (like the chinese mopeds), but is more car like. You'd actually have to disassemble the engine and take the block to machine shop to get bored out.
Oh and btw - in Europe and Japan Ruckus is called Zoomer, and does come with fuel injection. Just not in USA. And they received next ZoomerX model, while we are stuck with old Ruckus from early 2000s labeled as a 2022 model.