Harder makes some great tubes. I don’t know about availability here in the US, as they just don’t seem to have any footprint here. They generally outperform Photonis in most areas, but not sure how they stack up against the likes of L3 and Elbit for lack of real data.
Also, AFAIK, Harder tubes are expensive as hell. Maybe as much or more than high-spec L3 WP tubes, so penetrating the US market on a losing value proposition is a tough sell.
I’d be up for getting a couple just to compare.