The best way to get faster is seat time. The next best way is to analyze your seat time and find where you're losing time. Using just your phone, every app on the market seems to only store data as fast as the selected GPS, which with your phone GPS selected means you are limited to 1Hz. I went with Harry's and an OBDLink MX+ and was frustrated because steering and throttle inputs, as well as track position, are just about impossible to analyze because a 1s resolution is a huge amount of time on track.
I purchased this and it works flawlessly as an external GPS with Harry's Lap Timer. Now, I have both the OBDLink MX+ and this GPS as sensors in Harry's and the difference is night and day.
I took a few screenshots from Harry's from my fastest lap at MSR Houston with the phone GPS and then my fastest lap at ECR with this GPS and I've put them here for comparison.
Hopefully it's obvious from the photos, but the increased precision allows you to actually see your inputs to a much greater degree.
As a person who only recently frequenting the track I decided (like many people) that using my phone for lap timing was the most cost effective to start out. While I'm no stranger to logging engine data to see how a car is running, it took a few times to really figure out what data I wanted from going to the track. However I quickly found out that my phone (as new as it was ) wasn't quite up to the task of delivering what I needed.
Looking through logs of my different laps I found that I couldn't quite tell what path I was taking around the track. The data points weren't frequent enough to where I could always understand what path I was taking around a corner, as regardless of where the point landed you still have a reasonable distance you have to guess where you were. I could be wrong but Harry's laptimer seems to be setup to only record data in time with the gps signal, meaning it doesn't matter how frequently speed/gforce data come in, it'll only record as fast as the gps data. On my home track where most laps are going to be below two minutes one sample a second means that you only have 120 points of data, and a lot can happen in a second, (I know I've made mistakes that make me spun off track in much less than that). Having learned from engine management more data is more better, I wanted to find a solution to learn where my screw-ups were losing time.
I messed around with some other options but a lot of them required add-ons or made temporary mounting options a pain to figure out and it was harder to justify something more expensive without just holding out to buy a complete digital dash of some kind. My first few laps with the haze GPS I was slower than my last trip to the track. Over the early days of quarantine I spent some money on my car (responsibly?) And wasn't quite used to the setup yet. That being said my gps was faster than ever, recording every second of my less than stellar performance in glaring 18 (and sometimes 20) hz.
Using Megalog Viewer I compared my new laps to my old ones, it literally painted a complete picture of my (unsurprising to my family) lack of commitment. Rather than seeing 120 points of data I now had hundreds and I could see exactly where I was at corner entry (usually too slow) and corner exit (usually too wide).
My recent trip to Gridlife NOLA I was still getting used to the new data but could now easily compare the options between my more aggressive corner entry speeds and the ones that actually worked to see where the clenching wasn't actually needed because a slower smoother approach worked better. It made it much easier to come up to speed (hah) on a track I had never been to previously as I could easily compare the sections where I did better with clear results.
Without the massive increase in data available I feel like I would have been driving a bit blind for the last bit, or would have ended up spending significantly more on something that would spend most of it's time sitting in a closet waiting for my next track day. At the price, it's a no-brainer that this is a clear and obvoius step to take as you get more active at the track.
My track position data went from a bunch of squiggly lines (and very inaccurate times) on the map with my phone's internal GPD to a very smooth, accurate line with the Haze GPS. I am able to compare different lines lap to lap and see what affect they have on laptimes. Quality product at a great price!