For me it's the same as the old elevate sensor. But your results may vary. 

Tested yesterday. F6 with HRM PRO chest strap Vs. F7X PRO.

Runnig - First 15 min was F7X PRO 15-20 HRM higher  than I tightened little bit more watch stap and it started to be almost on same HRM as chest strap. But when I became run faster, F7X was very slower with reaction...

So wrist senzor on F7X PRO is much better than on F6, but if you want an accurate info during intervals still way better to use chest strap  ;-) For long activity with stable effort it will be ok

Well, the sensors on the watch cannot work better than chest straps. buy a breastplate and not bother yourself. the sensor on the watch is suitable for low activities and sleep tracking, no more

Apple watch is reasonably accurate when compared to a chest strap.  So there is no excuse that Garmin can't have a decently reliable wrist based HRM.  Based on everything I've been reading on reviews it serms Garmin has failed to produce a HRM that is at least as good as Apple.  Will probably wait til the Fenix 8 comes along before I upgrade 

I guess I'm one of those people that OHR just works for no matter the sensor model  or manufacturer  I would be hard put to tell the difference in accuracy between the 4 Garmin watches in my possession, various Mio and Polar OHR sensors and an apple watch. Seems to suit some people and not others. For that reason an updated OHR sensor would not be a reason for me to upgrade but it may be for you.

Do they react instantly to sudden jumps? with interval training?

No wrist heart will react instantly. For that matter neither will a strap but a strap will always be better. Physiologically, the heart does not respond instantly either; it takes time to ramp up and drop down. 

I completely agree with you, why then all these comparisons with Apple?

Who knows? Apple has its problems just like any other brand. But some here would have us believe that Apple is the holy grail. 
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