They both have their advantages and disadvantages. Depends upon the use case.
Old slide advantages:
able to distribute a load over a longer travel distance
old slide disadvantages
outside track easily bent and made useless
heavy
can take up more room than you think
again, really heavy
New slide advantages
lighter
less likely to bend and be immediately useless
longer lengths!
two very different configurations possible
New slide disadvantages
hard to get long stable throws. You can’t depend upon the track feeding back into the plastic slider once it has left the housing
point of hold over a small distance of the plastic slider is not as good as the metal in some configurations (e.g. on an angle)
plastic slides can get lost (comes with two kinds, but you only use on type at a time so the other tends to get lost)
plastic slide holes weaker than metal contacts and can get worn out
plastic slides not sold separately
Disadvantages of both kinds:
the torque difference between 12 tooth and 36 tooth gears is very great making linear slides slower than you would like since you go down to the 12 tooth gear often. More gear options are available in other lift types. Need a happy medium with a high strength option placed on the “in between” row of holes.
Mainly because we have only a few new ones available and the best place for the old ones is under direct power because they seem to have more friction with any kind of offset loading.