Is medical marijuana use a felony in States here it is legal?

That depends on whether you're asking the federal government or the state government.

Generally anyone who is just buying enough for their own personal use wouldn't be charged with a felony if caught. Felonious cannabis crimes usually involve an amount of cannabis over a certain quantity, selling or distributing or growing for sale/distribution.

I'd recommend against crossing any state lines with cannabis in your possession. You also don't want to fly with cannabis.

The federal government has no interest in pursuing individual medicinal users.

It's illegal everywhere under federal law. But if you live in a state where it's legal or at least legal for people with a medical prescription, don't worry about filling your prescription. For maximum safety, I suggest using it only in a private place such as your home. Federal agents are not going to bust into your home just because you're using medical marijuana in small quantities.

It is still illegal under federal law even in states where it is legal. It isn't a state crime at all and the feds aren't going after people in those states where it is legal though that could change at any time.

It remains a federal crime--even in states that have legalized it. Presently, federal prosecutors have adopted a policy of looking the other way in those states, but on a case-by-case basis, they can always opt to prosecute someone and sometimes do. If you're caught on federal property or in areas of federal jurisdiction in those states, including air planes and airports, the federal prosecutor will charge you with that federal crime. Also, if the feds have someone they want to get in those states and that person has a marijuana card, that's probably cause for them to get a federal warrant to search that person's house and arrest them on federal drug charges for any marijuana they possess.

What they are saying is it is legal at the state level, but not at the federal level. However, filing federal charges is unheard of for personal use. Federal charges are generally reserved for major offenders.

As long as you are not in possession on federal property, you will be fine.

It is still a federal offense, but as long as you keep it in your state or other states that have MMJ laws, no one cares. Don't take it to federal BLM land or any federal property. The FBI and DEA have better things to do other than busting someone for a few grams.

No

It is still a federal crime in all states.