I own a Series 3 which I purchased new in the 80's. It was high end then and THE detector to have. Found a lot of coins and relics with it.
It was and still is a fine detector. I can't tell you how it compares to today's low end (Ace 250) as I only buy high end. The ID function was a relatively new feature at the time and the depths which you could ID coin types on the analog meter was pretty shallow. It did not have tone ID, pinpoint mode or digital ID numbers as well as other features on today's detectors. The older units did not ID good targets around trash as well as today's units.
My feelings on this - if this is what you can only afford- enjoy it and have fun. You don't need to have the latest and greatest to find good stuff. However, if you do get addicted move up to a later model as soon as possible. I had to buy a hipmount carrier for my Series 3 as I could not handle the weight for a full day of detecting. Today's models such as the Ace 250 are light and a pleasure to use. Just the weight is reason enough to consider today's models. You will also have other issues to deal with - repair? battery issues- other size coils needed but not available- etc on older models.
HH
George