Engl Hardtailer Trem Block System

Like someone else already said, the idea is great but the execution not so much. I'm going to say pretty much the same but from a bit different point of view.
That other person said that the mechanism is stiff. This is only partially true because of why is that. And it is like this because it's overengineered. This is high quality product where the quality became one of its weaknesses. It works stiff because of it's insane tolerance levels and it being made of metal it sufferes from slight flexing. The cavity of the guitar never being perfectly planed (especially after being painted with electric paint) which, if screwed too well, causes the unit to flex and those super slim tolerances then become zero making it very hard to change positions. The only remedy to it is to play with screw tensions so it becomes absolutely flat. Then it works super easy.
As for the screw changing positions.... can't say much but true it's not stiff enough and it wouldn't suffer from having a lock screw or something...
The problem with the screw touching the block and touchpoint becoming resonanti is a true thing and only remedy to it is to raise the spring tension.
Another problem, not apparent with the usual setup is the fact that the unit itself (baseplate) is 2mm thick and screws are not flat tops (have small bulge) which make them stick almost 3mm up. If your springs lie pretty low (close to the bottom of cavity) the springs will definitely bite with screws. I had to recess the cavity by 2mms to accomodate for that.
I agree that this unit could only be used with D-tuna or something when you have to resetup guitar if you want to go back to regular FR operation. Although, I'd recommend using a piece of wood as a shim which you can have virtually for free.
This unit is heavily overpriced. Half of what is currently retailed for is too much, let alone regular price.

A great product in concept but poorly executed.
The brass fine tuning screw is very loose and constantly moves as you play, so when the time comes to engage the hardtailer it will no longer be in the correct position and your guitar will go out of tune. I also do not recommend using the tremolo at all while the hardtailer is engaged, as this also causes the screw to move a lot and make the guitar go out of tune as you're playing. On the contrary, the sliding mechanism is extremely stiff and unpleasant to use. The pull mechanism to engage the hardtailer is uncomfrotable and will hurt your fingers with the amount of force required to move the stiff sliding mechanism.
The hardtailer is advertised to have "no rattling noises" however there is a lot of loud rattling noise between the brass screw and the tremolo block whenever you pick hard, there is also an annoying clunking noise of the tremolo banging against the screw when bending strings or using the tremolo (which again, I don't recommend as the guitar will go out of tune).
The only good experience I've had with the hardtailer is using it to completely block the tremolo under high spring tension so the brass screw can't move and the tremolo can't move to create the loud rattling noises caused by the hardtailer, but this isn't what the product was designed for.
I recommend seeking alternate solutions for temporarily blocking your tremolo.

That product is great.
I had some doubts before ordering.

I thought It could negatively impact the sound in a blocked position.
As it turns out, the only slight problem is that if you bend too hard, there will be a noticeable sound (tremolo will clash against the blocker when you release a bend, when you bend, tension will increase and Floyd will elevate against the blocker).
However, you can solve this problem by slightly readjusting the blocker once in a while. I have noticed this problem ONLY when changing the tuning of my guitar without readjusting the blocker.

The benefit of blocking tremolo and dropping my guitar with a d-tuna-like product outweighs my cons.

Hardtailer can sit in the way of springs, so be aware of that too.

Install was a bit nerve wrecking, but worth it.

The screw does not move on my unit, maybe Engl has added thread locker such as Loctite 222. I have not checked.

It fits under the trem springs in my case. However, this is going to depend on the thickness of your sustain block. You can try sliding a 3mm hex wrench, under the springs of your guitar, to check.

Overall I am very happy with this product, but I wish 2 things were better.
1. It is stiff to lock and unlock
2. The provided screws are magnetic, which is acceptable, but not desirable or necessary in this application.

Compared to a Tremol-no, this is the better product. More dependable, does not unlock itself.