Yeah, it is real time. Its low/medium/high priority suggestions are some of the most accurate that I have found, so if you are looking for a site to just tell you a fee to use, then it's probably your best bet. They seem to correspond to somewhere around 1.2 MB from the tip, 0.8 MB from the tip, and 0.3 MB from the tip, respectively.
Having said all that, I still think there is no real substitution for learning how to read the mempool yourself and decide where you want your transaction to go. Fee estimators generally only estimate based on a current snapshot of the mempool and do not take in to account the recent mempool trend. If I want to be in the next block or two and the mempool is rapidly filling, then I might want to aim 0.1 MB or even less from the tip. If, on the other hand, there are very few transactions being broadcast at the moment, then I might be happy to go 1 MB or more from the tip. At the moment, that difference is between 80 sats/vbyte and 15 sats/vbyte, but could be even more pronounced, which could translate to a saving of several dollars or more.
This website is very good.
I agree that the most important thing is to learn how to read the mempool. This is why observing the mempool in a chart like that, with the transactions grouped by fee rate, is the best way to determine what is the most cost-effective fee to pay.
I did something very similar to what mempool.observer did
here.
You can select a fee per byte and plot your transaction in the mempool. Then you will see how many blocks (or bytes) you are away from confirmation. The mempool is very quiet now, and a 1-2 sat/byte fee would be enough for a quick conffirmation