My guitar students are always trying to get me to help con their mommies into buying them more stuff, so I always get the "what do I NEED?" question. And I am hugely fond of both cheap drum machines - they're a lot more fun - but mostly delay pedals, squeaky-clean DIGITAL delay pedals with a long delay - you WANT it to play back what you just played! All the Digitech "RPXX50" and "RPXX55" pedals have a 5 second delay, way adequate. The advantage of these over a metronome is that everything is working at once, you're learning harmony*, you're learning tone*... you're learning the secret to speed. Which is, that every note in a fast lick has to be played with it's proper duration. If you work on one lick, you can get one appallingly fast in a week - really! - but you speed up and slow down within the lick, so the "speed" is inapplicable in any other note grouping - you just have one fast lick.
With a delay, you can work on playing the exact same lick in a bunch of different locations, string groupings, NPS's... speaking of appalling, it's amazing how bad you suck when you first try to chase down some comprehensive speed by doing THAT stuff. But with a little work, it actually starts to teach you the 4-NPS vs. string-skipping parameters, alternate picking vs. "slip-picking" or "efficient" or whatever it's called this week. When I figured out my brain was incapable of some of that stuff, the delay pedal taught me how to use the Morsian cheat - if you just plain CAN'T make your head stick with very strict alternate picking, over 3 and 5 note patterns that get you backwards & inside out all the time - grab a note with your middle finger to get back to down-up-down-upland. Of course Morse doesn't use it to cheat, he uses it to be even more ridiculously-great. Dick. I use it to cheat.
You can pick up old weird Yamaha & Boss drum machines for $25, $30. There really hasn't been changes in the basic architecture of them for 20 years or more. And a Digitech RP150 used for $50 or $60 - the delay alone is gonna cost you twice that if you buy a "dedicated" delay-only Digitech "Hardwire" delay. They take the same "AudioDNA2" chip, stick it in a Hardwire pedal and program it to do 1/50th of what it does in the RP255 etc. Because stand-alone effects are "better".... With $450, you can buy enough Hardwire pedals to duplicate a $99 RP155! I think there are even some of those DNA2 chips in the new plastic RP's, you just want to NOT get the 100... 200.. 300 series, get the _50 or_55 ones.
I wouldn't be too surprised if them Axe-FXII's have some sort of delay in there, maybe. Did you see what they just released? Now, there's the NEW Axe-FXII ULTRA! And next year, the super-ultra! Then the Super-Duper ULTRA Plus Triple-Whoompie! Inevitable. Dicks. If I order an Axe-FxVII now, I'd have the money to buy it by the time they make it?
I've gone the "delay" thing mumplified by umpteens - a serious case of looperitis. I have the Boss VF-1 feeding a T.C. Electronics Ditto X2 and the RP250 feeding a Pigtronix Infinity and, Mr. Koltai made me a special 5-banger footswitch so I can keep the looper up top. Watching guitarists crawl around on the floor is pretty funny, except if YOU have to do it. And all feeding a 10-band mini-mixer, with the trusty Boss DR660 drum machine banging away. The good thing is, these loopers finally SOUND GOOD. I have a Boss RC20XL that sounded like crap unless you fed it a fully processed signal, and then you immediately get too many gain stages when you get circular = looping loops. And the Digitech loopers are like the Boss, they keep adding more features without fixing the basic 60's transistor-radio TONE of the innards of their base unit. Some looper features are pretty dumb, at least for me. Electro-Harmonix makes a big deal out of their half-speed feature, you can record a bass part at double-speed then drop it an octave with the 1/2 speederite. Ummm, I have like three or four pitch shifters... and the auto-quantize feature is basically so you don't ever have to work on timing?!? :icon_scratch:
*(Assuming your brain's engaged. Oops.)