nowadays managers cheque does not guarantee cash anymore they still have to wait for the clearance. I would suggest just use your personal cheque let the cheque clear before getting your new car. I just bought a new innova last week using a personal check. I paid last thursday and friday afternoon they wanted me to get the unit. But I didn't have the time so I got it on monday instead.
I paid in cash. I still had my old car then. So, medyo safe. When I got the Innova, I drove it and my wife drove the other car. Kung wala akong car, I would pay in personal check, wait to be cleared, and get my new car.
Unless the company has the same depository bank as your MC, there's a 3 day clearance period with the MC if it's drawn from one bank then deposited into another bank. The MC is better though as it is already considered a "funded" check where the account is debited the amount once it is made unlike a personal check where the funds are debited when the check clears or is deposited.
Also, banks are strict in issuing MC's if you're not a client of theirs. This is so as there are some unscrupulous individuals who purchase MC's, make the payment to an unsupecting buyer then they call in the check stolen and cancel it (amongst some).
You can also put a minimal DP in cash then MC the balance. Pwede rin fund transfer if you have similar banks.
We paid in cash for my first car. And then cheque na lang, same as what vinj said - pay reservation/min dp para reserved na yun unit(esp. if its a unique color or model) then use an MC. Mas convenient ang cheque sa kin, I'm not comfortable carrying loads of money around. tsaka no looking at your back for a robbery hehehe. It just takes time for the dealer to clear the MC, usually 3 working days.