If the TV is a modern LCD screen, using an upscaling device like the Framemeister will indeed greatly enhance the image quality on screen when converting 240p signals from RGB SCART into a 720/1080p HDMI output. the difference is stunning, almost as good as a CRT.
But if the TV is a CRT then there is no need for an upscaler since the image will already be at its best possible quality.
Having a CRT gives you the best possible image and is the more practical, cheap and easy option. But a CRT will occupy much space and is a heavy device. When you got a room dedicated to it it's the best option. I understand as well that when not living in Europe or Japan grabbing a good CRT TV with RGB SCART input can be complicated.
If you don't have much space or if the TV is used also by modern devices you may want to use an LCD, then an upscaler can help with the image quality.. But it's more complicated since you have to configure it, your consoles have to be RGB compliant and sometimes it requires modding. If you use a SCART splitter to plug multiple consoles you have to make sure all the cables and the devices carry RGB signal correctly. Upscalers are great but I want to warn you that it's not just "plug and play". And a Framemeister for example is more than $300, it's not a cheap option.
You can have an idea of what a Framemeister can output on a LCD screen if you watch
this capture on 720p60 quality + full screen, I captured this using a genuine Genesis console.
Having a good retro setup these days requires dedication whatever option you choose, but that's the best way to enjoy those retro games we're collecting, right?