You seem committed to be an owner of a 21. You don't mention your depth of boat knowledge or where you arrived at your destiny to own a 21.
First, for most people, there is a significant difference between the the 21 and the 21EC . Simply put, the 21 has been a basic workhorse for years, and the 21EC gave us the upscale version.
Baz gave you a good list of some of the idiosyncrasies of the 21EC. Your usage of the boat will determine which of those is most applicable to you.
For some people the 21 is a "step-up" boat for a beginner....for others, it is their one and only life long craft , and then, perhaps , the 21 is the downsizing boat that completes a long boating life.....pretty extreme, but that is the lure of this boat.
You are, apparently, a new poster and new member here. By all means, you are in the right place to learn what you need to know about 21 tugs. Learn to use the search mode and you will find an incredible amount of knowledge and insight.
Once you have prepared yourself with this info, your shopping will uncover 21's that were trailer queens with so few hours on the clock you won't believe it. Others will have been lovingly used for hundreds....even thousands of hours...and some , even relatively new boats, will have been neglected or abused.
When you find that potential boat ,your level of boat technical knowledge will let you decide whether you can properly assess the condition . If you are not sure what you are looking at, a professional survey would be in order to give you some confidence you are not buying some ones problems. Marinas and banks and insurance companies may help find a list of marine surveying specialists near you.
You are looking at a great boat with a minimum number of "systems" on board, but, as with all boats, there are still areas that will need inspection and due diligence .
Here's hoping you find that perfect 21 and enjoy it as much as I enjoy mine.....