Congrats.
It's worth whatever amount of disposable pocket money you have with which you're willing to part.
I'm the original owner of a Service-Six, myself.
I don't have the original box anymore, but as I recall it was listed as a .357 Magnum 4" Heavy Barrel Model. I had the grip frame modified to RB, and had the guys at MagNaPort do a Duty-Tune (and then promptly installed the factory mainspring upon its return), and let them port it while they were at it. Fast-handling, accurate, smooth and with the lively balance of a "short" 4" duty gun.
Nice medium-framed, medium-bore DA revolver.
I was disappointed when the GP series replaced the Security series (and remain so to this day).
I stopped doing more than occasional range quals with the Service-Six because of how nice my SP101DAO demonstrated itself to be (once I'd identified and corrected a burr that was causing it to seize after several cylinder loads of 125gr Magnum rounds).
I'd let the MNP guys try their Quad-Porting on it, back when that was a new process (and they assured me I'd like it and not want the barrel replaced). While it does offer the same potential disadvantage for some close range/retention shooting, when fired at reasonable extension it allows for some excellent muzzle rise control.
I've demonstrated to a bunch of other revolver guys how the little 101 can be fired as fast as the trigger can recover, remaining "on-target" without muzzle rise. Sure, the same amount of felt recoil force is still being delivered to the palm of your hand (which makes 158gr & 180gr loads still rather
impressive), but the metered set of ports lets the muzzle remain level during rapid shot strings (but still with all the attendant muzzle blast/noise you expect from porting). I forget the figures they quoted me all those years ago, but they said the amount of velocity lost was surprisingly not bad.
One of the guys I let try the gun at work has been trying to talk me into selling him that 101 for years. he used to own a similar size 2.25" 101, but never cared for the muzzle snap/whip when shooting Magnum loads. He was amazed when he tried mine with 125gr Magnum loads, and had a hard time believing the muzzle/sights remained on-target when rapidly triggering the gun.
I've always wanted a TDA 3" 101, though.