Hiking Thakgil vs. Fimmvörðuháls

I am planning a trip to Iceland for my family next summer (2026) and just learned about hikes in the Thakgil area, which looks absolutely beautiful. Rather than hike the full Fimmvörðuháls trail, I was thinking that we might prefer to just hike the waterfall section of the Fimmvörðuháls trail on one day and then hike one of the Thakgil trails another day. I've been worried about the need to prebook transportation for the Fimmvörðuháls hike, because the weather might not comply and because we'd need to worry about our hiking pace and timing. My impression from pictures is that the Thakgil area has somewhat similarly dramatic mountain scenary as the section of the Fimmvörðuháls trail near Thorsmark. And I understand we can drive our own 4x4 rental car there. We'd then be able to choose the best weather day while in the area to do the Thakgil hike, and my understanding is that we would not need to worry too much about weather the day we'd do just the waterfall section of Fimmvörðuháls, Is this a good plan? Will we be missing out not doing the full Fimmvörðuháls hike? Is there a reason why Thakgil is not more popular?