Here's some info from DOC's FAR forum on the CE-525 that you might find useful in your judgement:
From the CE-525 Limitations Section:
The Model 525 is not type certificated for “more than on required crew member” as applies to pilot-in-command proficiency checks in accordance with FAR 61.58 when operated by a pilot-in-command with a CE-525(S) type rating. Cessna recommends that the pilot-in-command complete an FAA approved proficiency check as required for more than one required pilot operation by FAR 61.58, regardless of whether the airplane is operated by a single pilot with CE-525(S) type rating or by “more than one required pilot”.
Except where otherwise prescribed by applicable operating limitations,
Minimum Crew for all operations:
One pilot, provided:
a. The pilot holds a CE525(S), single pilot, type rating
b. The airplane is equipped for single pilot operations as specified in the Kinds of Operation Equipment List in Section Two of the FAA Approved Airplane Flight Manual.
c. The pilot must occupy the left pilot’s seat.
One pilot and one copilot provided:
a. The pilot in command holds a CE-525(S) or CE-525 (second-in-command required) type rating.”
From the FAA AFS-640 FAQ site:
QUESTION 1: Situation is the CE-525 is certificated under Part 23 and as such can be flown single pilot by those that have CE-525S type ratings if certain equipment on the airplane works. Should the pilot only have a CE-525 type rating OR certain equipment is inoperative where a copilot must be used, must the copilot meet § 61.55 and secondly must the PIC be required to have accomplished a § 61.58 check?
ANSWER 1b: Ref. § 91.5 and § 61.58(a); The answer is yes, the PIC would have to meet the PIC § 61.58 qualification requirements. Although I'm quite aware that the verbage in § 91.5 only states:
"No person may operate an aircraft that is type certificated for more than one required pilot flight crewmember unless the pilot in command meets the requirements of § 61.58 of this chapter."
Now the question is whether we could get an NTSB Law Judge to rationalize the phrase "that is type certificated for more than one required pilot flight crewmember" means the same as saying "that is operationally type certificated for more than one required pilot flight crewmember." WHO KNOWS! Your guess is as good as mine.
But until we're shot down by an NTSB Law Judge, the FAA's position on these rules [i.e., § 91.5 and § 61.58(a)] require the PIC to be qualified in accordance with all requirements of § 61.58.
QUESTION 2: The question that arises is does the pilot that gets his or her type rating single pilot (CE525S) then meet the § 61.58 requirement for having accomplished a proficiency check in accordance with § 61.58(d)(2)?
ANSWER 2: Ref. § 61.58(d)(2); Yes, provided the practical test was accomplished with an SIC. But no, if the applicant only demonstrated single pilot proficiency on the practical test.
QUESTION 3: Additionally, if a pilot comes through FlightSafety's approved § 61.58 recurrent course as a single pilot, does that person or should that person get a § 61.58 sign off in accordance with § 61.58(a)(1) or (2)? Some concerns on this is that if the recurrent training will not meet the requirements for the § 61.58 check some or many pilots will forgo the training. Additionally, if we require a copilot during recurrent to issue the § 61.58 sign off then most pilots will opt for that, train as a crew and then go fly single pilot. While at first look these appear to be financial concerns raised by FSI which would have no bearing on our decision a closer investigation reveals them to be real safety issues that could impact training decisions of many pilots.
ANSWER 3: Ref. § 61.58(a); Yes, provided the § 61.58 PIC check was accomplished with an SIC. But no, if the applicant only demonstrated single pilot proficiency. And no, a checkride accomplished where the applicant only demonstrated single pilot proficiency cannot count for a § 61.58 PIC check..