As for semi-auto rifles, such as your ARs, about 99% of the current mag locks on the market became illegal earlier this year. They are still legal until the law goes into effect on January 1, but after that they are NOT a legal solution. Assault weapon registration, which is usually closed, will open because of these new laws. So IF you have the rifle in the state before January 1, you can register it and then no mag lock should be required (the implementation of these laws has not been publicly stated so it's not set in stone yet, that is just my current understanding of how it will pan out). The other option is use one of the mag lock options that will still be legal (Bullet Button Reloaded as an example) or to go featureless (Monsterman grip as an example). Like with the pistol, there isn't constructive intent in regards to assault rifles so you can always bring your uppers and lowers in separated until you get them registered or get them configured appropriately. If you're overly concerned about the legality of owning a complete lower with no mag lock, a rimfire upper can be installed on an AR lower with no mag lock and it is a legal configuration even if you also own a centerfire upper.
Low post count forced me to split my response into two posts. Sorry.