I've used one for 5 years or so, and have the latest-gen pod as well, here are some things to consider:
Broadly, I love it. Yes, pace/HR are just fine on flats, but as soon as you throw hills and/or wind into the mix neither of those are ideal. Having that one number (in practice it doesn't matter whether or not it's "measuring" or "estimating" power) to immediately quantify how hard you're running is great - 300W is 300W, it doesn't matter if I'm on flats or going uphill against the wind.
I principally use mine outdoors, but it works perfectly on a treadmill as well.
Some things with nuance:
Stryd is very precise/repeatable for pace and distance, but you'll likely need a specific calibration factor to get the accuracy right where you want it (read: 1 mile being measured/reported as 1 mile). You might need a different calibration factor for different models of shoes, as well. Yes, this can be a bit of a pain and is less than ideal, but it's not terrible to put up with.
Despite the above, training based upon effort/intensity and time is better here instead of by pace and distance. Stryd (and other platforms if you choose to use them) will give you a power they expect you to be able to hold for specific times - I use those power targets instead of pace.
So I'll translate "marathon pace", "5k pace", etc. to what wattage is says I could hold for those times/distances and hold that for my workouts and pace is what it is. This is great because it allows for doing workouts on hills, into the wind, etc. and knowing the intensity is correct and that you're not overcooking things as conditions change.