I never tried out a silent piano. However a friend of mine considered buying one but he gave up. The reason was, he told me, that there is a mechanism what blocks the hammers to hit the strings (for silent playing). He said that the key feeling differs therefore for acoustic playing and silent playing. Because the hammer way is reduced, so that the strings are not touched. Although this happens when the hammer is released from the action, he felt a pretty large difference in the behaviour of the action.
The digital sound is not the problem, some sound better than acoustic pianos, especially if the grands are small and not really grand.
If the piano is used as acoustic piano however, the key feeling is like a normal acoustic piano, so this disadvantage (how small or large, I dunno) is only there during silent playing. At least one should check for the action difference, maybe the development is now further, so that this is no problem anymore.
At one point, ideally right before the hammer hits the string, the jack escapes (echappement) from the action, freeing the hammer part of the action which travels by its own built up speed from there to eventually hit the string and fall back in to a catching system to prevent the hammer from bouncing back and forth between the string and the jack. (god I know all the dutch terms but my english piano nomenclature sucks)
It is true that a regular silent piano stops the hammers from hitting the string by means of a stop bar, not altering the action in any way, except shortens the travels of the hammers by 1-2mm (so they don't hit the strings) This system can be built into any existing piano or even grand piano as long as the piano tech that installs it is very skilled. (Korg produces a silent system, Technics used to, the most famous one is from Pianodisc, but imo it is not as good as the other two)
Now the trick to regulating a regular silent piano is to make it so the moment of escape comes a bit more early then you would normally do, which is not perfect for acoustic mode, but will still be sufficient (only noticable if you already knew the instrument before with optimal regulation, which it hardly never is) and this will still allow for enough escape to have a normal "natural" feel when in silent mode, where the hammers travel about 1-2 mm less.
So your friend is right. I have seen silent pianos where the stop bar was so horribly placed and the piano so badly regulated that the jacks didn't escape at all and you could literally push the hammers against the stop bar. This will give the piano a horrible touche which is comparable to how an organ feels. Mind you, this is only the case with badly installed and/or regulated instruments.
Yamaha silent grand pianos (afaik only the newer grand pianos) also use a stop bar, but when you pull the lever the action also gets altered so the moment of escape is always optimal in normal mode, or silent mode. This is why these instruments are so expensive, almost twice the price of their regular counterparts.
EDIT and slightly OT: the linked G1S is a piece of garbage though, I believe its not even made in Japan, but in China. I have played on several and even regulated 1 G1 and I cannot recommend them to anyone except the people that insist on having a grand but have no room to house one. And even then there are better instruments with the same footprint.