Is Matek Systems 2.4GHz ExpressLRS ELRS ELRS-R24-D Diversity Rx worth buying ? Is SKYSTARSRC SUPREME EXPRESSLRS 2.4GHZ DIVERSITY RECEIVER W/ TELEMETRY better ? 

I think latter one is discontinued ...

I don't think the Skystars has been discontinued, but US stock seems low right now. The R24-D is fine too, but be aware of the crystal offset issue. Make sure you get a version with the gold bind button, and remove the caps as described here: https://github.com/ExpressLRS/ExpressLRS...ency-Error

If you're not in a hurry to buy, there should be several new ELRS diversity receivers on the market soon (including true receiver diversity vs antenna diversity).