May be a little late, but I just tried it out.  A few items that I’ll be submitting feedback for once I find where to do so:

Positives:

It seems more reliable.  I am already having fewer random weird issues on it than I do with Synapse 3.  So the reliability at least seems like it will be more stable when it’s no longer in Beta.

Things I’ve noticed that need to be fixed, and that are very annoying if they aren’t fixed:

In Synapse 3, key combinations are able to be assigned and then work.  There are still bugs in key combination assignments.  These include the fact that you can’t create any combination with alt without creating a Macro now, unlike Synapse 3.  This is annoying for me as I use a lot of combinations with alt as I use my devices for productivity.

Similar to the first item, Synapse 3 would not perform a key combinaion while you’re inputting it, whether it was as a key combination or as a macro.  Synapse Beta does.  This is slightly annoying.

Copy/Paste does not work while setting a time in macros.  I’m pretty sure Synapse 3 allowed this.

Lighting effects do not work on the mouse when using Hyperspeed Multi-Device Pairing.  This is pretty annoying and is an obvious bug.  I tested the device while plugging it in and unplugging the other device, and there were no issues.  It should be able to work with Multi-Device Pairing as well though.

One thing that may make a lot of people angry, but is simply just always a thing when upgrading devices/software is compatibility.  Exporting and importing profiles kind of works, but not fully.  This is understandable, and I won’t harp on Razer for this too much.

Other than this, in my short time using it, it seems to be more reliable.  So I’m looking forward to trying it when these bugs are fixed.