Safety - none. Its only about 20V
Child use - some controllers have child locks on them that restricts access to anything likely to cause hassle. I am not aware of an extremely basic child's controller but my 3 year old grand daughter uses my Massoth Navigator with ease.
Set up - basic set up is similar and pretty easy. Learning the peculiarities of the system is something you will have to do but that's half the fun.
LGB used to specifically state that you can run their trains without a decoder. Piko state that a decoder should be fitted before use on DCC. The difference is the quality of the motor. I often run my new (LGB) locos before the decoder gets fitted but I would not do it in the long term. I would not run other makes. The vibrations set up must eventually wear even the best of motors (They hum on DCC). I know the old LGB3 and the Massoth system run analogue - not sure which other ones do - not all do.
Can't say on reliability but it seems fairly rare that we hear of someones blowing up.
As for the best - that's easy - its the one I use of course, and every DCC user will say the same!
Best advice I can give is find a mate or club with one and have a play. Reading the blurb from the manufacturers is total crap - they only tell you what you want to hear. If you get anywhere near the capacity of most units I seriously want to see your layout, and your bank balance!
Finally, the resale value seems to hold up well, so buying secondhand, whilst still not cheap, does mean you can trade up without too much wallet damage. Just get a system suitable for large scale use.
Why do I use Massoth, Several of my my running mates use it.
