Mobile phone Or fitness Tracker?

Necessary? Not at all. Can it help if you're trying to eke out every benefit of your training? Sure.

I don't run any more, but I ride a lot. The only thing I use is my phone with Strava running, safely tucked into a jersey pocket until the ride is over.

It might be a help to track your pace over certain distances (or regular running loops) occasionally, getting and resetting your baseline. But what you're after mostly is being able to extend your long runs (at a comfortable pace) into the realm of 10+ miles before your event day.

Let's be clear that there's a difference between a fitness tracker and a GPS watch.  I'd advocate for a GPS watch with a HR sensor.

Is it necessary? It's not.  You'll be able to do a lot with knowing your paces from your phone combined with perceived effort.

However, I do pretty much all my run training based on HR.  It really helps me control my training and paces on each individual run, as well as scaling my efforts as my fitness increases over time.

By the way, good job on a 1:50 HM! Sounds to me like you have a lot of potential.

Not necessary, as others said.  Sometimes people become a slave to them, to the detriment of their training.  This happened to me.  The day I accidentally left my Garmin in a hotel room in New Hampshire was a good day, as it turned out.

Until and unless you really begin to push your personal potential as a runner (and most of us are nowhere near doing so) the formula for improving is very simple:  run as much as you can (i.e., fitness, health, and time permitting).  Most of the time (90%) run at an easy pace.  Occasionally run harder than that.  You can mix it up as you like.  (Some weeks you might do one run at a strong pace.  Some weeks you might do a session of intervals, or hill repetitions, etc.  Enjoy mixing it up.  Have fun.)

What's easy?  You should finish the run feeling like you could go out and do it again.  Right away.

By the way, the formula doesn't change much even once you are seriously pushing your potential.  It just gets more structured and you begin to make finer distinctions.  The HRM can be useful for the latter although it also introduces numerous complexities that you will need to learn (and if you aren't willing to invest the time and effort to learn them then it is really doing you very little good and possibly doing you harm).

For the former (structure) you are best off consulting a coach or following a well-tested published plan.  And even if you are not pushing your potential, such a plan can be helpful (but by no means necessary) to keep you honest and just to impose some general 'good structure' on your running.  Choose a plan that is suited to your ability.  For example, if you are currently running 25 miles per week, don't choose a plan that starts you at 50 miles per week.  If you have never run intervals, don't choose a plan that is heavy on intervals.  Etc.

Necessary, no, but there are definitely benefits to using aids such as a phone app/ GPS watch for pacing, and HRM if using them properly. All of this will help you dial in your RPE then the aids become acknowledgement of what your doing.  Last July I was roped into doing a Ragnar run relay and started training in earnest again after a few years of half-hearted training with no racing.  My old GPS watch was dead so I used an app on my phone. 

For pacing, you can enter your recent HM time in at McMillan Running calculator and enter a goal time and it will provide you training paces.  You can use your phone and an app such as Runkeeper and can have it audibly spit out distance and pace info for as low as each 1/4 mile interval.  I've done this on & off for the past 2 years, simple.  After runs you can look at the maps, mile splits, elevation and run cadence charts.

My wife and I picked up some discontinued TomTom Runner watches off of Amazon for dirt cheap at Christmas time.  I just used mine yesterday for the 1st time with a Wahoo HRM strap that I had.  I've done plenty of HR field testing over the past 12 years so am familiar with it all.  Just learned something that I should have known, my RPE is off and I've been running too slow, but it's gotten me to this point so now I can do some smarter training heading into my next run relay event in May.  For doing HR field testing take a look at this BT article.  BT also has HR zone calculator that can calc the HR zones based on the threshold result (Gear on upper right/Settings/Training log settings/HR Zone manager).

I don't pay a lot of attention to cadence.  Its more or less a natural thing that will increase as you run faster.  There are three ways to increase pacing; increase turnover, increase stride length, combo of the two.  I find I cruise at around 160-180 steps per min or so naturally, fast running I increase to 185-195.

Best of luck on your running, a 1:50 is awesome for your 1st time out and as you "mature" over time you'll be amazed how much faster you can get.  BTW, what's your next goal?

Oops! missed that this was an older thread.  I however didn't use a fitness tracker my first 30 years of running/  :-)