This is more a post for those newer to learning bass, like me, and it’s also something that’s been mentioned on the forum before, but I wanted to add my experience.
Basically I just want to say how beneficial practicing with a metronome can be.
I have tried before, using metronome mobile phone apps that weren’t brilliant, and not loud enough so it did not make me concentrate enough.
However, knowing my timing and control aren’t brilliant, I invested in a digital metronome with a line out, which I have routed to my amp along with my my bass. Brilliant!
I now have a clear sound that makes me concentrate on it when practicing.
If I struggle with a Josh slow/medium/fast workout for a B2B lesson, I use the tap function on the metronome to set the exact same tempo, and practice to metronome for as long as needed to get it right.
I would say that having only you and the metronome exposes a lot of things you may miss.
For example, I have now realised that as I am worried about my weak pinky fretting finger, I have found I rush getting set up for the next note using the pinky, and don’t play the previous note well, so the sound is stilted, and also play the next pinky note too early. I’m now working on that. Never realised till it was just me and the 'nome.
I’ve wired the 'nome with control foot pedals to start/stop/change programs and it’s the most useful thing on my pedal board.
100% agreed @Mark_UK
I still find myself either a little early or even a little late depending on the tempo and complexity of the piece I’m playing. I also haven’t been able to get used to tapping my foot to keep rhythm possibly because I play seated.
The drum machine thing on the Zoom isn’t too bad at all either.
I’d like to get a drum machine at some point, but I think for me, having nowhere to hide in terms of its just me and a short click from the nome and no other sound distractions, has proved very beneficial.
Actually I prefer the drums. By a lot.
Which brings out the important thing here - having a timekeeper while you practice, whatever you want to use for it, is really helpful. Agree with Mark’s points above. There was a while that I noodled around without drums, and every time I went back to using them I regretted stopping.
So, metronome, drum machine, whatever - a timekeeper will really help you.
I’m with @howard. I tried all kinds of metronome apps on my phone, some really good ones that I actually paid for, but they just weren’t helping me that much. It wasn’t until I got the drum machine that I really started getting into the groove.
Oddly, the drum machine also helped with my back muscle tightness. BONUS!
I did too, and it wasn’t till I got a dedicated unit that plugged into the amp, that I made progress.
Perhaps that is psychological, and having paid out for a unit, and having it taking space where a nice fun effects pedal could be on my pedalboard, made me think I had better use the darn thing! 
Seriously, messing about with a phone while trying to hold a bass isn’t the best. That’s why I chose the 'nome I did, for a few quid I could buy a generic two switch control footswitch for it, and suddenly mounting it on the pedal board was the way to go. My EQ pedal has dual inputs, so by routing the 'nome to that along with the bass, the sound of both comes out of the amp with just one cable to the amp.
I use all three. When I am just fiddling around, unamplified, I don’t usually have anything. I use drums, backing tracks, or even play to the song itself when practicing a song.
I do use a Metronome when doing certain lessons, especially when they are Rhythm specific lessons, I think a metronome if paramount for those.
And this is because that I do have some dedicated practice and do specific exercises specifically designed for use with metronome. some are counting exercises, and foot tapping exercises (of course, you can dial into a drum beat to do some of this, but the metronome really exposes mistakes, and the point of the exercise and specific practice routine I am doing is for eliminating mistakes, and IME, even simple drum beats and / or backing tracks can still cover them up to some extent), others are playing while plucking open strings, or fretting when you want to get challenging.
These practice / exercise are geared towards rhythms not covered, or only slightly touched in B2B, and can get quite complex. And trust me, I struggle with them, they are hard, but I am making progress, slowly, but steadily.
And, IMO and IME, metronome is important for some of these.
That said, I just use Phone App Exercises. If I am playing louder then the Phone Volume gets, or with headphones, I just 1, use a metronome app on the computer that I have my headphones in, or use the Aux In on the Zoom and use the metronome app off my phone, and use headphones from the Zoom, or from Aux In to the Zoom and rout it thru the Amp, and headphones thru the amp.
Of course, the iPad or phone down on the pedalboard would not be ideal on your pedalboard, and if you are playing thru your pedalboard ALL THE TIME (I don’t, I move around and use lots of different things to play thru), That little metronome is cool, you can tap it on and off with your foot, and that would be difficult to impossible with an iPhone or iPad on the pedalboard. Cool little set up you got going there Mark