Manual is a great way to start. I started with manual for the first few months just to see if I was interested in continuing with the restoration process before I purchased any devices.
I have a DTR. I also have the retainer and air inflation setup sold by Chuck (the guy who makes the DTR). I’ve found I like a variety of methods, rather than just sticking with one. I feel like I’ve reached plateaus with one method, only to burst through it when I switch to another method. Who knows—it might just be in my head—but I don’t discount the importance of placebo, especially when the name of the game is consistency and not getting discouraged.
What’s been working for me these days is a weighted stack setup I made to be used in conjunction with the DTR retainer. The weight comes from a stack of fender washers, weighing over two pounds, which are fastened onto a 6” bolt. Sounds uncomfortable, but its honestly the most comfortable method I’ve found yet—I wish I’d done it years ago. It gives a great stretch and doesn’t irritate my skin like the DTR can. (I had to cut back on DTR use around year four, when I began to develop a line of white scar tissue that ran along my frenulum. Technically, this means I was using the device with too much tension, but honestly it never hurt to wear and I felt my progress had stalled. I wear the DTR probably 15% of the time now, with the weight stack making up the remaining 85%.)
I’d recommend starting with manual, then buying the DTR + retainer once you’re sure you want a device. The DTR will give you great beginner gains, and has a lot of flexibility that allows you to do other methods. And if you’re like me, you’ll want to mix things up over the course of your restoration process, so that’s important.