You'll have to do the math and figure out what works for you. TFS will likely charge a higher interest rate, so the question becomes how much you'll really gain over the life of the loan if TFS gives you a $750 discount on the interest.
Here's an example... Financing $10,000 for 5 years (assuming no early payoff). If you can get 3.00% somewhere else but you get 5.25% from TFS, the "sample" rate that pops up in their financing calculator, then the 3.00% loan is $610 cheaper. That's close to being a wash and makes the value of the $750 incentive questionable. If you finance a larger amount, the value of that $750 disappears quickly. In that case, the only way the $750 deal works is if the TFS rate is very competitive, or if you payoff the loan in a fairly short amount of time.
Yes and no. On the superficial sense, yes, strictly looking at points, TFS can easily sway the calculation such that they win long-terms if one fulfills the life of the loan on 60 installments with no prepayment. Some people borrow money from CU/TFS/etc because they simply cannot afford the car and in your example, maybe the CU offers the lower rate, no instant kickback, and in the end, the tortoise wins. That's fine and all, and obviously I have no idea who said poster is and his/her financial situation.
That being said, a lot of people don't realize that credit union auto loans like to throw in a cross-collateral clause that can be particularly nasty if said member is so-so about paying debt off on-time. All I ask is that before people take out auto loans with CUs, they look to see if said Cross-collateral clause is in there (it often is), as you may not get the title quite as quickly as you thought you would. Assuming that poster pays off all of his/her debts on-time, CU or TFS are both fine.
Note: I am not making any political statement here since some politicians have a stick about ragging on the big banking industry. But, CUs are not necessarily this perfect entity either. Personally, I am not part of a credit union, so I don't know how often a "paid off" car retains a lien to use as collateral for say a mortgage or CC.
The other option is if you hate your dealership, just take out a TFS loan and pay it off when you receive your first monthly bill. I don't recommend that, but if the dealership were jerks to you, I don't know how much the TFS chargeback amount will be, but it'll happen.