Originally Posted by Ramon
Flying clamps tend to lose more tension than fixed clamps because they are anchored to another string, not to a solid base. Also, when you use the flying clamps on the outer strings, which are spaced far apart, the clamps have to squeeze the strings closer together, which also causes tension loss.
Ease of use and versatility are also better with fixed clamps. There are some string patterns you won't be able to do with flying clamps, like JET. People who use flying clamps often resort to double pulls, which loses tension. If you have a fixed clamp machine and some extra money, you might want to invest in a flying clamp in addition to your fixed clamps because it will allow you to do more patterns, like ATW. I really think fixed clamps are one of the most important features for job quality.
Jet was developed using flying clamps, note John Elliot in the 2nd picture down with his machine:-
He maintains his flying clamps are more accurate than fixed clamps.
That said I'd recommend getting a fixed clamp machine too