I want to know what the difference between running Tor on your native OS and running Tor on Tails if there is any. Wouldn't your ISP see you using Tor regardless of whether it's in Tails or not? I know using it on Tails leaves no trace on your HD but if you're worried about your ISP seeing you use Tor, is a VPN the only way to go about it? Trying to understand it from a technical point.
ISP will see you connect to a TOR node (your entry node) but they won't know what actual data moves in and out of it, nor will they know your final destination (market/etc). They only know the single node you're connected to.
This means your biggest weak point is time-correlation to your activities. For example, if ISP gives log-in and log-out times to TOR, and law enf is monitoring you and know that you made a purchase on x date/time and made a reddit post on x date/time and that you were logged into TOR at x date/time etc etc etc they can map it all together.