ORIGINAL: RedGN
Is one better than the other, meaning is single conversion better than double conversion or vise versa.
I'd say that when a mfg uses the terms in his entire line of RXs, he's telling you that he makes single conversions with lower standards than for his double conversion RXs.
And if you see a RX that doesn't say "conversion" anywhere, it's because it doesn't matter with that RX from that mfg.