All should be rubber domes, but each is different. Some Type 6 and all Type 7 have USB. Previous keyboards have Sun's proprietary keyboard protocol.
• I have not tried the Type 4, but I have heard that it should feel relatively good for a rubber dome.
• Type 5 is one I got to collect because it
looks great and is a classic, in the style of Sun's computers of the mid '90s. Does not
feel great though.
• Type 6 looks and feels cheap.
• I found Type 7 to be very passable for a rubber dome. The ones I have used were comfortable and not mushy at all. They can also be laid almost flat (almost like negative tilt).
There are keyboards of Type 5, 6 and 7 that have a
"Unix layout", similar to the HHKB but in a larger size. Some people do prefer that layout.
Look here:
http://www5f.biglobe.ne.jp/silencium/keyboard/html/sun.htmlJapanese web page with Type 4, 5 and 6, with force graphs for the switches. The linear slope near the bottom for the Type 5 and Type 6 is indication of them being mushy.
BTW. There is also a rarer keyboard called
Sun Compact 1, which is like a Sun Type 5 in tenkeyless form factor. Interesting for collecting perhaps.
BTW 2. If you do get an optical Sun mouse with three buttons, do make sure to get also the mouse pad that goes with it: The mouse would not work without it.
If the seller is in Europe, then I might be interested myself. Please do send me a private message with contact info.
(Not stupid question at all. This forum is about discussing weird keyboards and sharing knowledge, among other things).