obtaining insurance quote ....

I currently have my plane insured through LL Johns and the underwriter
is AIG Aviation. The renewal is mid April and I would like to obtain
quotes from Costello and Avemco to compare rates. In requesting a bid
from Costello, under the SSA group discount, I have been asked to sign
a form that has the following wording

This is to certify that effective January 16, 2009 Costello Insurance
Associates Inc. is my only
authorized representative for the purpose of arranging aviation
insurance on my behalf.
It is understood that most aviation insurance carriers will release a
quotation for my insurance to
only one agent/broker, and that by signing this letter I am
terminating the ability of any other
agent/broker to obtain a quotation or bind aviation insurance with
your company.
This letter will remain valid until formally rescinded in writing

I am reluctant to sign such this as my current is intact. Am I eing
paranoid? What have other folks done?

I am not picking on or faulting Costello, rather just trying to
understand how the insurance industry works and not void any existing
policy

Thanks in advance

Ron Gleason
DG303 N303MR