Express LRS is one of the next generation RC protocols that offer lower latency (more updates per second between the plane and the transmitter), and can work better over longer distances. It's more technically challenging to configure in most cases - where you set up everything via connecting to it via wifi or Bluetooth via a laptop or phone then set up a binding phrase. Most of the more common protocols use a bind button or putting in a bind plug, which is much easier if you aren't technically savvy. ELRS is technically better than most of the other protocols, but unless you are planning to fly longer range FPV, or flying FPV quadcopters and need the fastest response times, you are probably fine with the more traditional devices. For most on this forum that mostly fly line of sight, DSMX (Spektrum), Flysky, Frsky, etc are fine and they don't NEED the benefits of the next gen protocol. One nice thing about ELRS is that it is generally the same price or even less expensive than name-brand receivers. At this point there are not many choices for ELRS receivers with servo pins (PWM receivers). Radiomaster just released a bunch of options, but most others require you to solder the pins on yourself.
If I were new to the hobby, I'd probably go ELRS, but I work an Information Technology job and like new stuff. I would not recommend it to most of the guys at my local flying field.