I highly recommend contacting them if you have a real need and budget for storage. They are a legitimate company that provides high-quality solutions and support. It is not a boxed product that you just buy off the shelf. Storage is generally complicated. Blockbridge will help with design, configuration, installation, and HA validation. They also perform remote installs.
There have been quite a few positive comments regarding Blockbridge in this forum. They have solutions for high-end configurations, including OpenStack, Kubernetes, VMware, and Proxmox, which is likely why you see little in terms of reviews (it's not for home-labbers). They have a proper Enterprise product for datacenter applications. They monitor the health of systems remotely and respond to critical issues 24/7. So it's not just a boxed product but also a service (not SaaS—they provide support and monitoring). You aren't going to pick this up at CDW or Newegg...
When it comes to pricing, my own experience is that Blockbridge offers a very fair price for the solution's performance, quality, reliability, support, and functionality. Software and support are priced per TB per month. There are several different tiers and pricing models to fit different deployment scenarios. They are very transparent on the pricing. I think the sheer flexibility of their pricing is why it's not just on their website. It is not a low-cost product, but what robust storage solution with good support is? We have been through every nightmare scenario with other solutions (at least 5 of them), and I can say, without a doubt, that I would buy Blockbridge every time now and ignore other solutions on the market. I'm never willing to take the risk again. FWIW, we run CEPH for cheap and deep (i.e., object storage) and Blockbridge everywhere where performance and reliability matter.
Regarding documentation, they have extensive documentation and tuning resources for Proxmox in their knowledge base (I think there are links on their main webpage). That being said, their solution seamlessly integrates with Proxmox. You don't even have to interface with their system once installed. From my own experience, everything works flawlessly in PVE.
Looking back at this post, I initially responded about a year ago. I can update you that another year has passed with 100% uptime on all our deployments, including Proxmox.