I trust it as much as commercial grade APCs I've used in DCs. It definitely cost more in my engineering time than buying an off-the-shelf component, since I spent a lot of time researching it. But I'm a hardware nerd at heart and rarely get to putz around with this kind of stuff, so it didn't really seem like labor to me.
The precautions I took were probably overkill but since it wasn't my lab I chose to go pretty overboard. In addition to conforming to the strict charge-discharge guidelines Panasonic thoroughly delineated in their sheets, were to use 1: use "protected 18650's" (actually designated as 19760) which have internal circuitry to keep, say, cheap chinese eBay charge-units from setting peoples house on fire, 2: sourced the batteries from a vendor I've trusted for ages (since the Panasonic 'greens' have such a popular reputation, and knock-offs make it into all sorts of markets including first-tier shops like Amazon and Digikey, I asked my vendor to source directly from Panasonic JP, which he did and provided me with a packing slip). Fear of Li-* is reasonable, and I figure risking permanent damage to ones body and/or life isn't worth the 7 bucks you save buying no-names - go with the 19760's and live life to the fullest! (Pro-tip, the form factor of the 760s are about a mm or 1.2 mm or something longer than unprotected 850s due to the added circuitry -- which I presume is just a PTC thermistor + kill switch, I haven't looked it up though. I'm sure there's a mass difference too if you have access to lab quality scales or are friendly with your local cannibus vendor.
Thrown in the case I have a live K-type thermocouple in all 8 of the 1u's (a pair in each rack) with conservative failure policies should temperatures exceed parameters I set. I put put some nice fusing (HRC.. why? because I was already going overkilling and since this wasn't an off-the-shelf component, and I'm not an EE with extensive PDU experience I decided to go safe. (I also consulted with a post-doc buddy of mine who's actively in lithium battery research and after a good chuckle told me the precautions I took were satisfactory.) It came in at around 5k USD for all 8 units with everything, including ~115 a piece for the Hammond 1u's. Each unit can sustain a little under 4.5 kVA which gives more than enough buffer time for a graceful shutdown
How did your tests go with this? I'd totally use a system like this - properly packaged up of course. Li-ion and Li-poly make me nervous.