Most of the major streaming apps like Netflix and Prime Video use Dolby Digital Plus audio. The Beam (Gen 1) doesn’t support Dolby Digital Plus. It only supports Dolby Digital. Since you have a TV equipped with eARC, I would go with the Beam (Gen 2) so you will be able to get the highest quality audio from any streaming app you use including Dolby Atmos audio. The Gen 2 also has improved dialog clarity which is very important when using a sound bar.

All that @GuitarSuperstar said is correct. But if all you want is a significant improvemen on your TV sound, and have no intention of buying a Sub or surrounds, the gen 1 could do that for you.

Thanks John.  As mentioned, I'll be using two play:1s as surrounds, so hoping that will really improve the sound.  

Thanks GS.  I'm thinking that for the sake of £100, I'll be better off getting the gen 2.  Maybe not a massive difference in performance, but still better?  Hoping that using the play:1s as surrounds really improves the experience.

Not important for the OP, but to clarify, you don’t need eARC to get dolby digital plus, as it’s carried over ARC as well, including atmos.  Also, if you went with Beam Gen 1, you would get dolby digital out of your streaming sources.  I still would opt for the more current Gen 2 though.

Given how rapidly technology becomes obsolete, you’ll get more useful years out of your purchase by purchasing the current model.

There are alternate strategies. For example, with a newly introduced industry standard, the first wave of product is typically more expensive and there may be some yet to be discovered bugs that may not be fixable by a software upgrade. An example of this is the wave of HDMI products where the chip design that virtually every manufacturer’s product used were defective. There was no field fix for this. Holding back on purchasing the first wave is a strategy to avoid this possibility.

Another scheme is more frequent purchase of last year’s model. For example if the current model is ‘A’ and last year’s model is ‘B’, purchase a used ‘B’ selling it as ‘B’ slides into ‘C’ status and purchase the current ‘B’ while your ‘C’ still has some value on the used market. Currently, SONOS units hold their value very well.

Thank you all for your help. 

I will be buying the gen 2 when it is back in stock.  Hoping that with the play 1s as surrounds, I'll be suitably impressed :)

Really appreciate everyone's time.