In my short career in the home brew world I've always transferred the beer from the primary to bottle without a siphon (directly from the spigot). I've started to see that this made my beer darker and with unwanted components(oxidation). So I'm deciding now between an auto siphon or a CO2 cylinder and etc for a closed system. In that sense how the two compare to each other in terms of oxidation prevention? If possible a comparison in terms of percentage would be great, like a closed system offers 0% and an autosiphon 30% prevention (something like this). Does the expenditure on the cylinder and the needed gadgets really worth the investment? Tks!
If you intend to get into kegging, then absolutely go for a CO2 setup. CO2 transfers are easy and kinda fun. If you're only doing this for moving the beer around, a CO2 cylinder and regulator are way too expensive and bulky.
Autosiphons work incredibly well. Coupled with a plastic clip to hold it in place in the bucket, plus a bottling wand on the siphon tip (valve in the tip that allows beer to flow when you push it against the bottom of a bottle), and you've got a super easy and cheap bottling setup. You'll need only one hand to hold the bottling wand, and have a hand free to hold and move bottles around.
You could also just attach some tubing to your spigot and put a bottling wand at the end of that. I think I would still go for the autosiphon though. Since you're bottling from primary, you have more control in avoiding the trub and yeast in your bottles.
An autosiphone is a cheap effective way to do it. $15, give or take, and you'll be in business. You won't find an advantage in terms of oxidation of one vs. the other. I've done both, and have both. The autosiphone is still pretty straight forward and quick to use, and I still use it despite having CO2 at my disposal.
If you get a tank, regulators, fittings, etc... you'll be into it for $200, so I wouldn't do it unless you're building a kegerator.