Cessna 510 Citation Mustang
The smallest Citation ever is clearly a derivative of the Cessna 525 CitationJet, but has distinctive characteristics. To start it has wide, oval cabin windows, not squared off. Secondly the Citation Mustang has different cockpit windows, somewhat like that of the Raytheon Premier I. Finally the baby Citation has ventral fins.
Confusion possible with
When viewing the Citation CJ1+ (and older versions) and Citation Mustang side-by-side you see they have a lot in common. However, the CitationJet family has different cabin windows (a bit squared off top and bottom), different cockpit (side) windows and no ventral fins.
When looking closely to the Epic Elite only the general appearance and the cabin windows may put you on the track to mistake an Epic Elite for a Citation Mustang. For the rest they are significantly different.
Raytheon Premier I
Apart from the general appearance and the cockpit side windows there are many differences between the Premier and the Mustang: the shape of the cabin windows, the pointier nose, no ventral fins and a more rectangular tail cone, to name a few.