I had researched this route prior to a trip to Hawaii, but wasn't sure if my schedule or weather conditions would line up for an attempt. This is not a route to try in wet conditions and it's almost always wet here. I rolled the dice one morning and ended up with beautiful weather - partly cloudy, no rain, and from the looks of it not a lot of recent heavy rainfall either. Water levels on the jeep road were manageable - up to the knees in some spots - and there wasn't a lot of mud either. So the first 4.7 miles were mostly uneventful, I enjoyed the scenery and tried to take it easy. Beyond the water diversion things got a lot more fun - there's a real nice bamboo section, then lots of muddy/scrambly trail sections, with frequent water crossings for the first mile or so. It seems like there is a fair amount of foot traffic here and I saw lots of sections where you could either travel in the river or on either side of the river (rocks or mud trails). Many trails veer off into the woods or up the hill, I think those are mostly hunting trails, so care must be taken to stick close to the river. It is a lot of "micro navigation" though - the GPX tracks don't really help you pick a side of the river, you really need to rely on sighting the trails. Prior scouting of the trail or having a play-by-play trail guide would help a lot - I ended up wasting lots of time hunting for trails, backtracking, or by picking slower routes. To me it feels like following the river/staying in the water is more fun, more dangerous, and slower - so you have to decide what matters most to you. After a mile or two the official trail ends (at what is sometimes referred to as the Blue Hole, a waterfall). I didn't have much trouble finding the trail from there though - and while it might be a bit steeper in some spots, it also seemed a little easier to navigate. The back section doesn't have a lot of alternate routes and you spend less time in the river. There are a few sections where ropes have been installed, mostly around slippery rocks and steep inclines - overall it felt pretty safe. Towards the end things start to open up a bit and you can just navigate by line of sight. The views at the top are incredible, I took a few minutes to just soak it in and enjoy the experience. Saw a couple helicopters buzzing around here which didn't detract much from the beauty. Turned around, headed back down, which was more of the same - very fun but also got a bit dangerous in spots as my muscles were tired from all the water scrambling. Took some falls but nothing major, breathed a sigh of relief when I finally got to the water diversion again. Saw a few groups of people at the water diversion - some horseback riders and a few folks that had driven up most of the way there in jeeps - I was the only one on the trails beyond that point though. The jeep road is sometimes closed but on this day the gate was open, and on the run back down the road I saw another 5 or so jeep parties, which in the context of this island is very popular/crowded.
Gear - overpacked/overprepared a bit, just in case. Kept the phone in a waterproof case and didn't use it much. Brought 2L of tailwind and a filter but didn't end up filtering any water. Wore trail running shoes to start and packed a (heavy!) pair of Tabi shoes to change into for the water sections. I did not end up using the Tabis at all, which at times felt like a mistake - lots of slips and falls - but I hadn't trained in them and wanted to power through without them just to see if it was possible. So yes it's possible to do this route with normal trail shoes if you have dry conditions - but I don't recommend it. Also brought some gloves to help on ropes / rocks, but didn't end up using them.
Overall the course was everything I'd hoped it would be, one of my all-time favorites. Just know what you are getting into - the inherent risk is high and even if you are trained, prepared, and careful, things can still go wrong here. A solo + unsupported + on-site attempt would be more hubris than bravery - there are plenty of videos and guides out there on hiking the trail, at least check those out before the attempt and know what you are getting into. Also read the horror reports about folks who had to get rescued or got injured or killed.