Long time ago I used Tetenal liquid emulsion, and results were ok. I see it is no longer in production, on Fotoimpex site I see that they have ADOX Polywarmtone Emulsion and ROLLEI RBM Black Magic 2.
Anybody used one of these? Do I need to user hardener? With tetenal I did not used it, and it was just fine.
Sorry, can't comment on which to purchase but I'd personally start with the cheapest option and upgrade if I feel it's necessary after some tests.
AFAIK the hardener is optional and would be helpful if you do things to the coated emulsion that can soften or harm the gelatin. E.g. toning or very long wash cycles.