It depends on your riding. For what I do, I wouldn't need all the (expensive) bells and whilstles.
The YSS emulsion shock has a single adjuster which I believe incorporates compression and rebound.
The standard Fzs1000 shock has separate Compression and Rebound adjusters, albeit not very effective.
I'm not sure the £300 YSS would be any better than the standard FZS shock, which incidentally could be rebuilt by any half-decent suspension shop, costing around half the price of the YSS.
The 2008-2016 R6 shock is on another level, about 90% as good as a £800 Nitron R2 shock (a long time ago, I had both shocks so could directly compare). With suitable length dogbones it would cost somewhere around the £150-180 mark, wouldn't be expensive.