As with all things 'it depends'...
Before the Cannular can seamer, the only available canning machines were eye wateringly expensive. The Cannular isn't inexpensive, but it is within reach of homebrew use. I purchased mine when it was offer and a couple of hundred pounds less than it now, the current price would have given me more pause tbh.
Cannular Compact Semi-Auto Canning Machine
The splash guard in my view is over priced, and I use the panels of polyurethane foam that it came packaged in as an impromptu splash guard. The biggest annoyance for me is the recalibration of it, which in theory isn't necessary for many but the temperature swings winter to summer here in Scotland mean that for the tiny gap required between the rollers, that thermal expansion makes a difference, once dialled in though it is a dream to use, fill, add a lid, press a button, done.
Regarding the CO2 purging, since there's little to no headspace in a can, you cap on foam or onto liquid itself, it is much less of an issue than with bottling. I chill down my beers to as low as the fridge can take them, give the cans a burst of CO2 from a fill tap to the bottom of the can then fill either straight from the kegerator tap or a party tap with a length of 3/8 tubing to the base of the can, then cap and seam. If I haven't chilled down further than usual, it still works to can usually though there might be some extra foam. It is fast and fuss free, and I'm a bit of a fan of it. My few annoyances are not being able to find the 440ml cans which I'd like to use, that my adhesive labels seem to crinkle up after being applied, and that my canning machine is on the other side of the garage from the kegerator which means I have to carefully carry full cans between the two.