Note that save-boosting things like Resilient Focus (+2) and a ring of protection (+1) will help you with the suit's downsides. Also, most of these save-ends things are actions you take on *your* turn, which means you might save the very same turn before you've every experienced a downside.
Finally, in Epic you might consider Martial Resolve, which allows for a save at the start of your turn (like a Warden, which I presume you are not), giving you yet another chance to avoid the effect.
All in all, I think the downsides are managable, and in fact likely to be less bad than a until-the-end-of-your-next-turn effect.
However, I also think the PP power's aren't strong enough to really warrant a downside. It's a bit of a strikerish PP, and it has a fairly easily obtainable prereq, so it's comparable, say, to the Thuranni Shadow Warrior. That one has an encounter single target attack that probably does more damage (two-strike weapon vs. NAD doing 1[W]+Dex and an effect each), and few good other powers and a decent features.
Basically, the steamsuits strength aren't really the powers; those aren't that special. You're going to do it for the suit itself - the AC is quite decent, and it's easily accessible to classes with poor defenses - it could be a really large bonus for some. Also, it's not that easy to become large, and being large can enable cool things like one-handed reach weapons (e.g. a greatspear + shield is a +3 proficiency bonus reach weapon with great feat support).
However, taking damage just 3 times is a very low bar to reach. Aura's, ongoing damage, auto-hit stuff, attacks vs. NADs, multiattacks... There are lots of scenarios where the suit can become damaged very, very quickly.