I'm really not keen on the Eclipse as a personal ship, it's so ridiculously slow for an M3 - any enemies are off your radar before you can catch up to them (bear in mind that combat missions will generate hostile/target ships based upon your combat level and your current ship class, if you have an M3 and an average combat level you will by and large be up against varying numbers/waves of M3-M5s in missions, and the Eclipse is the slowest of all of them, you'll be at a distinct disadvantage in for example timed assassination missions and escort missions) - it's ok if you're going to shoot a couple of missiles (something cheap like mosquito, they do at least have a decent cargo bay for missile storage) to get their attention so they come to you, but IMO they're really not that fun to fly and combat comes down to either trying to get them to come to you, or watching them disappear into the distance - if you're wanting an M3 for dogfighting you'd be better of stripping them down and selling them so you can buy something a little faster IMO - the Split Mamba is better in terms of action, it's shields aren't anywhere near as good but it's very fast and agile, the Argon Nova Raider is a superb player M3 with a good balance of speed, shields, and weaponry, and if you can get one (they're not for sale, but there's an unclaimed one that you can get for free in the vanilla game and you can sometimes capture one from pirates if the pilot ejects) the Blastclaw Prototype is a well shielded M3 with 4 front mounted weapons (if you can get hold of any, put Plasma Burst Generators in those 4 slots, they're short range but very powerful) + 4 turret mounted weapons, an absolutely ginormous cargo bay (650), and although it's not the fastest ship, it has a bit better speed (159 m/s) than the Eclipse and its other features make it far better ship to fly.
The Eclipse does have uses - they are ideal for short-range station defence under AI control (once you have your own stations), escorting your freighters, or because they have a decent cargo bay manual trade runs of expensive high-tech low-volume goods such as crystals (or once you have stations of your own, selling high-tech goods that you have produced, or moving them between stations), or to patrol a small area or sector - but as a player M3 I don't really rate them highly.