I think the Phenom 100 is geared toward the Mustang, not the CJ1+. That said, it splits the two pretty evenly.
According to May 08 B&CA, the Mustang is $2.766M while the Phenom 100 is $3.287M. The CJ1+ $4.755.
Mustang max cruise is 339kts, Phenom is 380kts.
The Phenom has a larger cabin than the Mustang.
The Mustang has more baggage than the Phenom.
The Mustang will have superior TOFL numbers.
The Phenom has a MMo of .70M while the Mustang is .63M.
Over a 600nm trip, the Mustang will take 4 minutes longer than the Phenom, but burn 162lb less fuel.
When compared to the CJ1+, the Phenom 100 actually has a slightly larger cabin.
The CJ1+ has fewer cubic feet of baggage, but hauls substantially more weight. This is because in the CJ series they don't make allowances for baggage near the lav.
The CJ1+ has about 100nm more NBAA range with 4 passengers than the Phenom 100.
Cessna Citation parts and support are widespread in the United States; for these Embraer products it will likely take longer and not be as easily obtained.
**IF** the Phenom 100 and 300 live up to their performance claims, they could potentially put a hurt on Cessna and the Mustang thru CJ3 line.