Crippling a horn because it's a pain to fix it right seems like an unfortunate approach to repair. For a situation where the instrument was rescued from the recesses of the attic and little Bobbie is going to play it in band because it's all that the family can afford, I suppose arguments could be made that; the kid won't gain from the added feature, that he could care less about the instrument's authenticity, and that the likelihood of the mechanism going out of adjustment during rough handling from a fifth grader makes it a liability. This is much the same argument that was made for disabling the D connection to the F# cup (a fingering which frequently gets used for many arpeggios which include both D and F#- covering a fair amount of ground).
OK for a horn set up for less than fully responsible kids.
The Eb trill really just isn't that hard to set up and is not particularly less stable than the A/bis regulation.
The Eb trill cup pivots (on most horns) on its own inch and a half or so hinge rod. This, given a level tonehole, makes it very simple to set up to close and seat perfectly. Its protected location makes it unlikely to get smacked. The hold open springing can be set very light.
The weak part of the linkage is the touch on the arm that arcs over the E cup with a foot in the back to activate the trill cup while the bottom of the touch presses the E cup shut. (The foot to stub of the trill cup hinge rod is a great place for a thin strip of tech cork covered by a layer of 2mm teflon sheet for both smoothness and to avoid compression at the linkage) On many mechanisms the arm pivots on a very short bit of hinge rod which is subject to developing play quickly, allowing lateral movement at the touch, and is so short that it's a pain to swedge.
The True Tone altos are an exception to this as the arm pivots off a forked set of hinge rods (as in the A touch or bis mechanism in many horns) so that play has a much lesser effect in the adjustment and develops much more slowly. Still a pain to swedge should it develop
The most painstaking piece of the whole deal is simply ensuring that the E cup closes via the felt under the touch at the same time as the trill cup is closed by the foot on the other end of the arcing arm. This is a painstaking adjustment to be sure- but generally slightly easier than the A/bis synching.
If there's lateral play in the arm, given the sloping nature of most E cups, it's going to be near impossible to achieve without requiring a firm grip closure while playing. Works fine but clearly not ideal. No play in the mechanism? Works like a champ with a feather touch.
My one point five cents based upon simple repetition on many horns and subject to refinement by those with greater insight- don't spend it all at once!
