In the past I never felt a need for a daytime flasher, but have had too many close calls with cars which concerns me especially when riding our tandem with my wife. For night rides we use a Magicshine with a large stem mount battery which I am pretty happy with especially after getting a new Hope universal bar mount for the light. I also have a Cygolite Metro 400 which I bought mostly for use on my bike since I didn't always want the big Magicshine lite.
So I have been using the Metro for a daytime flasher on the tandem. Its plenty bright enough, but it sticks up kind of high off the bars and gets in the way of my Garmin which on a K Edge mount in front of the bars. I would like something smaller and lower profile that I feel I can leave on the bike all the time. One option I found is the Cygolite Dart series which comes in 210 and 350 lumens. I am not sure if the rubber band mount will be good enough though. Also found some mounts for both a Garmin and light and put them out front of the bars which would be ideal, but the combination of the mount and light is too expensive. Thanks for any advise.

Just found this, it might be what I am looking with the 300 Lumen light:

https://www.guee-intl.com/products/imount

I have a similar light from a different brand to those dart's, rubber band mount works fine, mine even weighs slightly more than those, doesn't move at all.

Try a lightweight helmet mount light. It improves visibility to others, especially combined with a bike mounted light. I noticed this on other cyclists who use both bike and helmet mounted lights. The two-points of light enhance perceptions of direction, speed and distance.

So I began doing the same thing earlier this year: Vivo-Bike Illuminati on the front (supposedly 300 lumens on flash, with wraparound lens to enhance side visibility); Blackburn 2'Fer on the rear (non-directional, good side visibility). A pair of 2'Fers would do about as well, and recently have been available for less than $40 a pair on Amazon. These are small, lightweight, hold securely but are detachable for recharging, and last several hours on flash.

I usually run the white forward and red rearward facing helmet lights on flash, day and night. About the only time I turn them off is for nighttime group rides. However a few other folks run helmet lights in group rides and they don't bother me. As long as they aren't using something like a Cygolite Hotshot on full blast it's not distracting.

A helmet light gets the light up higher, above the roof line of most passenger cars, and closer to eye level with truck drivers. Bike mounted lights may be hidden by other vehicles and visible only within a narrow angle of view. Helmet lights show wherever you look -- when I see cars approaching intersections and parking lot driveway exits quickly I look directly at them. Gets their attention -- I can see them suddenly notice me, make eye contact and slow or stop.

Only a couple of times in the past year has anyone blown right in front of me despite the lights. A few weeks ago a young lady driving with her nose buried in her phone right hooked me. And a couple of nights ago, a guy who may have been drunk (he was coming from an area with nothing but bars and strip clubs) or believed his mission was more important than anyone else. He blew through two stop signs on a turn.

There are brighter lights, especially white headlights, but none I'd care to wear on a helmet. The Vivo-Bike Illuminati and similar models weigh almost nothing, so the thin stretchy rubber band mount is appropriate for the light and easy to snap on and off.

The Light & Motion helmet lights look good too, but are very expensive.

Use what you've got?
Mount the light on the underside of the handlebar. I have mounted several of my lights under the handlebars over the years.
... They tend to be much more stable position wise, 'hanging' from the bars (much less 'wandering' up and down on rough stretches).

...On cheaper (Magic shine clones) headlights the area where the power leads enter the light head is not really sealed for upside-down position in the wet. Easily remedied with some 'poster putty' and 60 seconds of time.

Here is another out front mount that will work with my Garmin and existing Cygolite Metro:

https://www.amazon.com/Rec-mountsTM-...DJX6B987K29HTP

I think this is the best option, I can move the K Edge over to my other bike which needs it.

Mounting the Cygolite upside down on the bars is problematic because it interferes with shift and brake cables.