I used them in-person and it was good. I don't really know what truly differentiates one company from another. They all have the same gouge and are going to prep you in pretty much the same way. The biggest caveat to any interview prep company is to not get too locked in on canned/memorized responses. The interview team can tell right away whether you are reciting lines you've been working on for weeks or if you are coming off naturally in conversation. The prep companies definitely give you lots of good tips how to frame your answers, plus how to sit and act in the interview in general. Just don't fall into the trap of working out line-by-line how you'd answer any particular question you expect to be asked.