Calcium Reactor recommendations

[daplatapus]

I'm looking for advice on calcium reactor experiences. I've got a Vertex RX-4. It's been ok for my existing tank but I'm pretty sure it won't keep up with my 210 upgrade. It appears they aren't making the RX-6 or are doing some upgrades, but everyone's out of stock. My next thought was getting one from RLSS, but alas they stopped making them too. Although it sounds like they're going to building them again, but there's no eta
Has anyone tried either the SRO 5000 or any of the JNS reactors?
What others would you recommend for a 300 gal water volume?