Do you want stronger or lighter? Your choice, with the usual tradeoffs. The Birdiepal Outdoor is advertised as “The strongest trekking umbrella of the world.” The Swing Liteflex is advertised as “The world’s lightest trekking umbrella of its kind.”
Euroschirm has a PDF catalog of their trekking umbrellas available here that may answer some of your questions. (The catalog link is on the left below the picture; the file is about 14MB.)
There is some confusion regarding product names, probably compounded by shifts in the company’s marketing strategy over its 90+ years of existence and the fact that it has produced umbrellas for other companies, reportedly including Golite.
The original company name is Eberhard Gobel. They manufacture various collections of umbrellas marketed for trekking, golf, business, travel, and promotions. Birdiepal and Euroschirm are brand names owned by Eberhard Gobel. I believe the Birdiepal line was originally marketed as golf umbrellas and the Euroschirm as trekking umbrellas. However, there seems to be a recent effort to consolidate their product lines under the “umbrella” name of Euroschirm and the Birdiepal url now redirects to the Euroschirm website.
The Birdiepal Outdoor and the Swing Liteflex are different models of Eberhard Gobel (Euroschirm) trekking umbrellas. Each is available in a variety of colors or with a reflective coating. You will find some online references to a “Birdiepal Swing Liteflex” (e.g., Campmor and various forum reviews), but a review of the Euroschirm catalog suggests that these designations are incorrect.
The Swing Liteflex is essentially the same as the old Golite trekking umbrella. Refer to this article and the associated reader comments, which include this quote from a Euroschirm representative: “The Chrome Dome was designed out of the Swing liteflex, but GoLite chose to cut alot of corners by using lower cost toolings in order to have the market and profit margin more manageable. So you can call the CHROME Dome the ‘younger cousin’ of the Swing liteflex.” I have both the old Golite and the current Euroschirm versions and can confirm that they are virtually identical. The current Euroschirm version has a beefier slider, a thicker handstrap, and a few minor cosmetic differences that add about 15g over the Golite version. The Euroschirm website lists the Liteflex as 207g; I read 222g on my scale. My old Golite is 207g.
I haven’t used the Birdiepal Outdoor, but the Euroschirm website shows it as slightly larger than the Liteflex and significantly heavier at 372g. My understanding is that the struts are basically the same but the shaft is stronger and the fabric is heavier with some extra reinforcement. There is an entertaining video on their website (also available on youtube) showing the Birdiepal Outdoor being abused in various ways. Looks basically indestructible.
I don’t often take an umbrella while backpacking but the Liteflex is plenty strong enough for anything I would use it for. If I was anticipating conditions requiring the extra strength of the Birdiepal Outdoor, I probably wouldn’t carry an umbrella at all. If you are considering one primarily for shade, the Liteflex would certainly be sufficient; the Birdiepal Outdoor would be overkill. (Note, however, that there is also a Birdiepal Octagon model splitting the difference at about 300g).
Of course, you could simply buy one of each and get the free shipping!
Happy hiking.