A PR company is built on its reputation, both with the client and with the press, as well as the results.
PR comes in 3 flavors!
1) Success with Happy Developers (Green? :D) The PR campaign was a success. You'll find the PR company links to these people and references you to talk to them. If the PR company does NOT have anyone you can talk to as a reference, avoid them (unless they're brand new and offering you some awesome prices, which may be worth the risk).
2) Failure with Happy Developers (Blue? lol ...) The game was a failure but the developers feel the PR company really did an awesome job and the failure occured somewhere else. The holy grail of a good PR person is having a stock of these types of clients. Not every game will be a success, but if a failure is still reccomending the same person it means they're clearly a cut above in terms of their service.
3) Failure with Unhappy Developers (Red) The game fails and the client is UNHAPPY with the service. Go out of your way to find these people, they won't be listed on the PR person's website so some extra searching will have to be done. Take it with a grain of salt and get details. Some people are unhappy because their game failed and it isn't the PR person's fault, but they're the ones that take the blame. Sometimes the PR person just doesn't do a good job AND the game isn't very good.
There's also the really odd case where the game does well but it has nothing to do with the PR person they hire, but I've almost never encountered that.
Anyway, to me I don't like the way these guys sound so far...
As to your original question: There's a bit of value in a simultanious launch IF the game is cross platform multiplayer. If not, there's probably very little extra value there. Any game that benefits from "economies of scale" - which in this case is a larger online population or some other synergy for having many people playing at once - then you want to hit the server as hard as possible on day 1. Otherwise you may not need to do a simultanious launch - BUT- and this is a big BERTHA sized butt:
1) Mobile games are hard to make money OR promote via PR (clever ad buying and high RPU is the easiest way to win here).
2) Steam games that are mobile to PC ports usually do very poorly (Bad reputation for good reason, why play a simple mobile game with a powerful gaming rig?)
There are two scenarios where things are a bit different
1) Your mobile game really does kick ass (Badlands) and therefore comes to Steam with a powerful following and fans (Win / win and you go take a Scooge McDuck Moneybath).
2) You wait to launch your mobile game AFTER Steam's launch in order to fool Steam users into thinking your game is not a mobile port. (Which will be MUCH harder now that they have refunds).
Not to suggest you go with plan #2, as it is shady and the new refund policy will kick you in the ass potentially - but that is a strategy employed by some people.
Hope that helps!