Here are some things to consider about the current situation on the Florida Turnpike. First, Toll-By-Plate is new and only available on a very limited section of the Turnpike. If you only access this section (mile 47 and south), you can use TBP but I have to wonder why anybody would want to do so. Toll-By-Plate will charge you an administrative fee unless you setup a pre-paid account. If you are going to go to all the trouble to do that, why not just setup a SunPass account and install transponders in your vehicles. I also question how well TBP will work and suspect this is why the Turnpike Authority is doing a test run first. For example, how will TBP work when you are towing and car or trailer and your tow vehicle plate is obscured? I suspect that many motorist are likely to get toll violation letters which they will then have to deal with.
My advice is to get SunPass. Even if you only travel the Turnpike once in your life, SunPass is a good investment. The mini transponder only cost $4.99 and they give you a $4.99 toll credit. Setup an account backed by a credit card or bank account and the system will automatically refill your account when it gets low. You set the balance at which refill occurs and the amount to be refilled.
A couple of gotchas:
If you are going to travel a long section of the Turnpike, and especially in a mult-axle vehicle, make sure you have an adequate balance in the account.
If you are towing a vehicle you don't want to get charged twice on two transponders. If the system sees two transponders go through it will usually charge both for the total axle count of the vehicle. So, if you want to have a separate transponder for your tow vehicle (for independent travel like side trips) you will need to get the portable, not the mini transponder. The mini transponder is a small credit card like device that affixes with adhesive to the windshield and is destroyed if removed. The portable transponder is bigger, and cost more (about $20 I think-sorry no toll credit) but you affix it to the window with suction cups. This way you can remove the transponder from the tow vehicle window when it is being towed so you don't get double charged. On request, the Turnpike Authority will send you a metalic bag to put the transponder in so it doesn't receive the toll signals. The other advantage of the portable is that you can move it from vehicle to vehicle, including rentals and friends cars. You could, of course, just use one portable and move it between the motorhome and your tow vehicle as required but I find that to be a pain. You also have to replace the batteries in the portable when it gets low.
Hope that helps. We live in Florida and travel the Turnpike almost daily. The new high-speed lanes are awesome though they (like TBP) aren't in place everywhere on the Turnpike yet. Where they are though it's great. You just keep moving at highway speed and the system debits your account. I can't imagine why anybody would waste time sitting in line to pay a toll anymore.