I'm using them and have been very satisfied so far. They are extremely fast, they trip instantly with no sparks. They work as advertised. I purchased four of them about a year and a half ago and am now using two of them with an expansion planned that will put the other two into service, hopefully in the next year or so. I am using them with the Lionel PowerHouse-180's which also have very fast breakers. So far the PSX's have always tripped before the PH-180's. However, to be fair here, the PH-180's have 10 amp breakers and I have the PSX-AC's set to 8 amps.
Manual reset is probably the only required add-on (as I see it anyway), but I have added manual reset switches, the alarms and indication LED's to my set up, but I am a sucker for all the electronic gadgets and bells & whistles. So far I am quite satisfied with them and think they are worth the added cost to your layout power.
In some of the discussions here some folks think they are waste of money and not required. I think that would be true if you are only running conventional with pre or postwar trains. However with the modern command control electronic engines (which is all I have) I think they provide some added protection. If they save the electronics in just one of my engines from having to be repaired or re[laced, they have more than paid for themselves.
I recently added some meters to the mix in my set up and had some unexpected results. Described here: PSX-AC's, PH-180's and analog volt & amp meters. I have corrected that by re-locating the meters in the circuit, but have no explanation other than the cheapie meters from ebay that I used. As I said in the thread, I may call about DCC Specialties (or Tony's Train Exchange where I purchased them) to see what they have to say about this.
This is the only odd thing that has happened with mine so far, and I did play with them on the bench for quite a while before installing them on the layout. I'm not an electronics expert like some here on the forum, but personally I would recommend them. With the prices of our engines these days, some added protection is very nice to have.