keep the magichine 880 on your mtb.
Get a specialised flux expert, can be had for 180 link this it the best road “ride fast on completely dark roads” light I have ever used, proper focused full/dipped beam behaviour just like a car headlamp you do not blind drivers. this is for the bars on your road bike. I have experimented with all my MTB’ing lights (1st gen magicshine, fluxient, gloworm) none of them are safe for road use – unfocused very bright beam is dangerous to blind oncoming cars, just think how blind/annoyed you are when the other guy doesn’t dip his headlights when you are in your car, these lights are bright enough to have the same effect as they are unfocused.
then get dx lightweight small XML-U2 or better for your helmet for mountainbiking, this is your head “see into the corners light” when MTB’ing. e.g. this one for 30 notes on DX link or if you have more budget to go branded / with support a gloworm X1 link (what I have) this has the advantage of being able to angle it down, so for road riding you can leave it on low angled down at your bars (See your gps / phone / whatever). and I am sure there are others (I last shopped for lights a year back). never point these type of lights at oncoming cars they are too bright will blind drivers.
finally something like a topeak headlux as a safety light on your head for added visibility in traffic.
a little over your budget but covers all bases, doesn’t blind drivers and gives you the full night riding mtb and road experience.