Although technically the Z27 is not designed for the Safari or the Al-Star, that is where I currently use these converters. The Z28 has the two little plastic nibs that keep the converter in place for the Safari/Al-Star, but the red accent clashes with some of the pens, particularly the Demonstrator/Vista.

While it is true that you don't see the converter when the pen is in regular, use the aesthetics even when refilling are a big part of pen use for me, so in some of the bodies where the red accent of the Z28 clashes (such as the more recent Al-Star Whitesilver), I go to the all-black Z27.

While the Z27 fits properly in the Safari/Al-Star, without the two plastic nibs that keep it in place there is in theory a small risk that the converter will pop out and result in a messy situation. I would guess it will take quite a bit of jostling or a fall for this to happen, in which case chances are you have bigger problems as a fall that pops the converter out would most likely have damaged the pen as well. But this has never happened to me and I've been using a Z27 in a Vista that has seen a lot of action (to the point that the Lamy logo completely rubbed off), for several years.

I am also very careful when refilling the pens where I have a Z27, holding by the converter as I twist its knob because sometimes if you hold by the grip and twist the knob, depending on the amount of friction, you might end up loosening the converter, making the whole converter spin instead of moving just the piston. Hopefully that makes sense.

It does not get a perfect score because of that one theoretical risk and the wish that at some point there will be a Z27 with the security nibs or a Z28 without the red accent.

I wouldn't buy a Lamy without the converter. They allow me to use all my favorite Diamine Inks.