Do not frequent here that often, so late answer, see also my answer on your other post. But short answer: no, it does not improve the C64 and no, it does not make it run smoother (the opposite actually). It is interesting though for other reasons, but see my other answer for details.

You mean C64OS? Well, it is meant to run with REU and JiffyDOS. Then it is already much faster. My assessment: First the pros: - it is a fantastic achievement. The amount of labour and love in it is much to be admired. That he created such a great body of documentation also on the C64 and the SD2IECcin general makes it even more admirable. - It looks great. It is well thought out. - With REU it can do real application switching. But the cons: - there is no real software for it. There are some apps, but nothing that a normal user would bother to start C64OS for. In that sense, GEOS is way more usable as there is actual software for it. - Without native software it becomes pretty much a fancy launcher to non native software. But why would you first start C64OS only to start non native software? - It is build around the SD2IEC. Which is defensible for a stock C64, as there is pretty much no other option as disk swapping is infinitely worse. Also, wit( JiffyDOS, the SD2IEC is actually quite fast. But the problem is if you get the modern hardware like the C64U or the Ultimate 64, as you then still need an SD2IEC on top. Which makes absolutely no sense as the Ultimate has superior own USB drive file access. I understand the reason: the Ultimate SoftEC file access is not compatible (yet, it’s being worked upon) with SD2IEC / CMD HD. And the C64OS author did not want to make something Ultimate proprietary, which is completely understandable given that when he started developing C64OS the Ultimate was still very niche, and the SD2IEC was what everybody had. But it is rally a pity as C64OS would fly using native Ultimate Command Interface USB file access. - As it needs a SD2IEC, it won’t run on a stock C64U. And it feels very unnatural to buy a modern C64U and still buy an SD2IEC. - It is sold at a quite steep price as physical release only. Which makes absolutely no sense to me. High price, ok, his choice. But why physical only? Not only is digital download much easier, but also buying the physical package caused me that I had to pay again the amount that C64OS already cost me in shipping and import duties. Makes no sense at all. Even not from a piracy perspective, because obviously the SD card has already been ripped by somebody to upload on some of the usual sites (will not name them).

By the way: a cartridge would bring a lot of other issues, mainly in compatibility. So do not agree that would be a better option. By far the best option now that new Commodore adopted the Ultimate architecture is to build an Ultimate Command Interface native alternative. USB file access via UCI is, although not as fast obviously as cartridge memory access, so fast it feels almosg instant. Combined with the REU that the C64U now standard has and its networking capabilities (which by the way both C64OS already can use) making a cartridge image out of it does not give much more advantage, and has the disadvantage of compatibility issues with existing software.

Have: - Commodore: C64, Ultimate 64 Elite 1, Ultimate 64 Elite 2, C128 flat, C128D, C128DCR, Plus/4 - Oracle Atmos - ZX Spectrum 128 Toastrack, Spectrum Next KS3 coming - Texas Instruments TI-99/4a - Atari 2600, 800XL - Acorn Archimedes A310 And several PCs (two Linux, one Win11, and Win11 corporate laptop) and a Raspberri Pi 400 running RiscOS

Only see this post now, but yes, proud owner of a working 1901 here. Have a second 1901 but that one does not work anymore (big puff of smoke so probably a capacitor). This really is THE ideal C128 monitor as it can do all the screen modes of VDC mode mania and also has the switch between 40 and 80 column mode on the front. 1084S is also nice, but was made for the Amiga, and you have to be careful with that one as not all 1084S types can do the digital RGB of the C128 and many models have the 40/80 switch on the back.

My own demo in the 1901 in 80x50 text mode.

Well, my by far all time favourite ever game is a Microprose one but not a C64 one:

On the C64 obviously this one: