A shifter's a fair bit more convenient than a velcro strap, especially when you want to stop briefly and do something with both hands (add/remove clothing, take photos, that sort of thing). I have an auxiliary V-brake on my Streetmachine that I use like a car handbrake (also functions as source of donor parts should I damage a gear shifter mid-tour). Unless you need it for legal compliance
[1], if you're happy with velcro, that's fine too.
Main advantage to having a rear brake on a tadpole trike is for handbrake turns when it's icy.
[1] If you've got a setup where a single lever operates both front brakes like barakta and Tigerbiten have, you need the rear parking brake as an independent braking system.