My boss and I disagree on our writing implement of preference. He’s a ballpoint pen guy. Today I was sitting in his office listening in on an extremely long conference call. I got bored and started fidgeting – then I ran across a Parker Jotter on his desk. The action on this BP is amazing. I really like the way this pen feels when you click/knock? it. It reminds me of the quality of a Pilot Hi-Mecha.
Does Parker make any MPs that use the same design or similar to the Jotter?
Yes. There are several variations to the mechanisms. Some are fixed with a c-clamp to the nozzle like the Caran D’Ache 844. Some are 0.5 drop-in units with a grey body. Some use metal bodied, non-refillable cartridges in 0.7 and 0.9.
The distinctive Jotter ballpoint ‘click’ is a result of their patented rotating mechanism that ensures the tungsten writing point wears down evenly. You won’t get this kind of feel with the MP models.
Darn. Thanks though
I like the jotter pens too. Its clicking is very responsive.
I also own the MP version of the jotter (plenty of colors to choose from in the market) and I think they are somewhat different feel in clickings due to the room of movement allowed is relatively small comparing to the pen version.
Yeah, they feel different but I still like the pencil version of jotter simply because of the shape of the body feels about right.
A lucid explanation 
It takes years of experience and observation to summarize a good answer. 
Let me add more info. for Parker Cartridge Pencil Lead Refill:
The 0.9mm cartridge is supposed to be non-refillable because PARKER wants user to buy a new cartridge to replace instead of refill the old cartridge.
User can refill it from nozzle.
The lead size is around 1mm so 0.9mm will work somehow but not a perfect fit.
The grey units come with a pre fitted spring that sometimes needs to be removed or replaced with a spacer so that the tip protrudes just right in the modified pen. I also usually remove the eraser nub to avoid accidental jams.
I have all the cartridge variations of the jotter, including the non-refillable ones—by the way, the eraser is under the external cap on the models that use those. I’d have to double check but I think they used the same model 5R eraser that Eversharp (which Parker ultimately acquired) used in their Skyline series.
Anyway, I have managed to refill the non-refillable cartridges before, but removing the steel ball bearing needed to open it, without damaging the top of the cartridge, is a little tricky. There are also “fingers” holding the lead inside the cartridge which apparently you can damage so they never advance the lead properly again. But it is at least possible to do. 
The later cartridges with the replaceable eraser and no clever attempt to seal them, are much nicer and work more reliably too.
None of them are as clicky as the pens, though.
