The only way to dim the Hotshot 50 is to set it to steady mode, no pulse, flash, blip or strobe. Use the rightmost button to adjust the brightness. Press once and it'll either dim or brighten; press again to reverse the process of brightening/dimming.

That's what I do for nighttime group rides. I also got complaints about the intensity of the Hotshot 50 in group rides, even on the slow pulse mode because it still peaks at maximum brightness. And I have two other dimmer red LED taillights, one built into the saddle, the other one of those combo LED/reflector doodads. Good enough for group rides.

In the various flashing modes the rightmost button only adjusts the timing, speed, intervals, not the brightness. They all peak at maximum brightness. When riding solo on public streets I set it to one of the more annoying strobing modes in daytime and switch to the slower pulse mode toward evening.

When riding on the MUP I turn the Hotshot 50 off completely and use my less bright lights. If I had only the Hotshot I'd use the steady lamp on dim. Doesn't take much to be seen at dawn/dusk or night on the MUPs. Our local city rental bikes have lights that most serious bike commuters would consider inadequate, but they're plenty visible on the MUP which doesn't have many nearby utility lights -- most of the lights are on posts at least 100 yards away or father.

I love my hotshot 2w. it came as a bundle with a cygolite Metro 360. I only had a 2 mile commute to work starting my third shift but i noticed a big difference between how close people used to drive close to me before and after i added the light. admittedly, i stopped commuting to work on my bike at night becuase frankly even with the light, people around here aren't very used to it and I had one too many close calls, but there's something to be said about the battery light versus brightness of this tail light. i rave about it.

its snowy and cold out right now. it would take a special breed to commute in this (definitely not me) but whne spring hits or as we get closer to warmer weather, i'll be using the lights again to commute to my new first shift job.

The difference between Cateye Rapid X3 and Cygolite Hotshot Pro 150 is the luminous flux of the lights. X3 is double as bright as the Hotshot Pro 150 and has a much wider beam angle for better visibility.
We Test Lights | Rapid X3 Rear Test and Review
We Test Lights | Hotshot Pro 150 Test and Review

Yeah, but you know what? Good enough is good enough. Once you've got something as bright and eye catching as the Hotshot 150, there's no real need to keep looking. Anything brighter is entering obnoxious territory.

Nope, I still wouldn't use the Rapid X3. I run 2 Pro 80's, which are already visible from half a mile away or better IN DAYLIGHT on Random Flash mode, and the mounting system is VASTLY superior than the X3. Also from what I can tell the Hotshot has better light modes, and the flashing pattern speed and steady pattern brightness are all adjustable.

According to these source, just a single X3 is visible from more than a mile distance. Doen't supreise, since a single X3 already has more lumen than two Hotshot Pro 80 USB together. Also one X3 is $30 less expensive than competitve 2x Hotshot Pro 80 for $80 together.
evanscycles.com/cateye-rapid-x3-rear-light-100-lumen-EV276557

The Spacer X allows to use the longtime common cateye rear light mount, which is very flexible.
CatEye Spacer X
CatEye America I CatEye America Small Parts Safety Lights
cateye.com/files/manual_dl/9/1172/TL-LD720-R-F_HP_ENG_v4.pdf

How do you define better?
Cateye Rapid X3 steady mode is adjustable in 4 steps, each side has its own mode/brightness control.
So combination of steady + flash/rapid/pules/vibration mode is possible.

There are two types of people in the world, cateye users and cygolite users...lol

And Dinotte users!
Steve