Winguru -- if you're still checking this, there's a lot of good information here. Flyingfemme in particular has summarised things very well.
Although not relevant to operating the Meridian, if your friend ever decides to buy something else that will fly above 25,000ft, his pilot will need the 'pressurised aircraft' sign-off too, i.e. endorsements for FAR §61.31(e), (f) and (g). It's something that once caught out an old colleague of mine after he switched between variants of the same aircraft family -- his original one being certificated to 25,000 feet, and the newer one to 31,000.
Not applicable in your case {to the Meridian}, but thought I'd mention it for completeness for anyone who might bring up this thread in the future.