Let's be honest - this isn't the star of Beppu's "hells" tour. Sure, the reddish-brown hot spring looks pretty unique (they call it "Blood Pond Hell" which sounds more metal than it actually is), but it's arguably the least impressive of the bunch. Still, you're here to collect 'em all, right? Don't skip your stamp!
The nearby foot bath is nice. Actually, the nearby steam-cooking restaurants are probably as interesting than the spring itself.
Think of it like Pokémon - sometimes you gotta catch the less exciting ones to complete your collection.