This pretty much defines how I work.
I “move slow,” taking the time to test carefully, and leave clean, concise, well-documented code, but I’m told that I actually move at a blistering pace.
I have found there is absolutely no substitute for having an operational, full-feature implementation (I hesitate to call it a “prototype,” because it needs to be fully functional, not just eye candy). I am not a fan of lash-up prototypes, because they invariably become ship code, and starting on a foundation of sand is a very, very bad idea. I short-circuit that, by writing everything as ship code; even my A/B experiments. I can often recycle the rejected code for other projects. It also saves a lot of testing time, as the code is being constantly tested from the start, and being tested while still in scaffolding (meaning more complete testing, overall).
For example, in the app I’m developing now, I’m working on a dropdown screen that allows the user to define search criteria for a database lookup. It’s a complex and fraught operation, and I’ve already had to make a number of changes, based on actually using the facility, as opposed to thinking about using it. If I had simply solidified my original design, it would have been a mess.
I will also be making sure that the facility works for different regions and languages, despite the first implementation being only for the US. It has been my experience that this kind of thing should be built in from the start, as retrofitting it is a nightmare (and bug farm).
My approach does mean that I often need to rewrite a lot of finished, tested code, or throw out big chunks (which is one reason I have a bunch of small, polished, standalone package projects). It’s taught me to design and implement very flexible code (which is actually dangerous, so I often go back, and remove flexibility, once I have settled on an implementation). Nevertheless, I have found it’s the best way to end up with a usable, relevant, high-quality, finished product, that meets the customer’s needs, in a remarkably short time.
DISCLAIMER: This is a viable way to design UX (the kind of code I usually write), but may not be the best approach for “engine” or algorithm code.