The 7 string lock nut is a flawed product to begin with, since it asks the middle lock block to cover 3 strings. That means it's pivoting on the D string. Sometimes if you don't lock it right you can have either the A or G loose enough to lose it's tuning if you slack the tuner. You can get enough pressure to lock the strings for whammy use by squashing the D down, so it's fine. But as a replacement for a Steinberger nut it's probably not advisable because it would be prone to slippage in my opinion. Plus the mounting method isn't really designed for long term 100% string tension. As a matter of fact it's not designed for string tension at all. It's meant to lock at zero tension and only accept tension during whammy use, which by definition is temporary. Even if you whammy like a madman during playing hours the guitar still spends most of it's time sitting without tension on the nut. It would probably be prone to pulling, compressing, and distorting the mounting holes. Top mount would be even worse. The Steinberger mounts with screws parallel to the string tension, not perpendicular.