Make sure you have already researched and hopefully had some test rides in Slingshots with the type/size of windshield you think you want. Much cheaper to know in advance that what you think you will work for your. Most windshields are solid and can deflect too much air from the cockpit if too tall. The MadStad Single Adjustable line of windshields allow the windshield to be raised or lowered to control airflow under the windshield into the cockpit, but can also allow rain to get under the windshield. MadStad offers a Windshield height vs Driver height chart to show what size windshield is recommended for a given driver's height - Slingshot (2015 - 2019) Single. Twist Dynamics now offers a windshield that looks to be a MadStad Single Adjustable and the MadStad size chart should also work for the TD Windshield. It never hurts to contact the manufacturer of any windshield you're interested in and ask them what size they recommend for your height and driving style (looking over or thru the windshield, for example).
While awaiting delivery back in 2015, I rode with a Slingshot owner who had purchased his Slingshot out of state before Texas started allowing sales. He had an F4 Customs +3 windshield and the test ride showed me it was too short as the top edge of the windshield sat right in my sightline and distrupted my view of the road. When my Slingshot finally came in, my dealer gave me a standard Blade windshield which, although it was a little short for me and allowed air to hit my forehead, I used for 6 months before finally ordering a MadStad 13" Single Adjustable windshield which allowed me to position the windshield high enough to look through or lift my head a little and look over the top of the windshield. I liked the adjustability of the MadStad windshield, but replaced it after I went boosted because I was afraid rain coming under the windshield might damage my AFR/Boost gauge. I now use a NASCAR-style Tallboy Plus 2 windshield from windshields, which I also like.