Riding for 10 miles would take about 30 min, what do you hope to accomplish with that?

It's too short to create any fatigue and you can learn to run off the bike with less than 3 mile runs, so why bother?

Is there something specific you're after?

Its called duathlon and its a lot of fun. But the majority seem to be more 2 or 3 mile run, 10-15 mile ride, 2 to 3 mile run. Not many longer ones.

I tend to agree with you. I saw this workout in a training plan and I didn't really see any advantage over a standard brick, but thought I would put it out there and see if anyone else had a different view.

Not sure for ironman, but I'm a huge fan or shorter, zippier Duathlon bricks. Something like 2-4 reps of 1k-5k-1k or thereabouts (sometimes 1mile-4mile-1mile). It's not something that I would do every week, but it's great transition practice, and it teaches you really well how to run off the bike and to get rid of the bike funk in the legs very quickly. Typically when we do these, the effort level is pretty high (sprint/olympic race effort). My favorite course for these (sadly is currently under construction) has a short but steep and punchy climb on the bike loop (the bike loop is just over a mile, so we usually do a 3lap bike) to change things up a little. I usually use these both in draft-legal and illegal formats with our group, depending on who is there and the racing they have coming up. The trickiest part for these workouts is finding a spot with low traffic (often prefer industrial parks on the weekend, or research campuses) and where you don't have to worry about bikes going missing during the runs (you can also either bring someone to watch the bikes, or do 4-5 intervals in which each person does 2-3 so that those sitting out a round can watch the bikes...), and that has enough sign posts or fence space for people to make transition spots (I'm working on building relatively portable ITU style bike racks that could fit in a backpack for the ride over to where we do these workouts, not there yet, but I've worked on a few prototypes)

Don't think it would be helpful for an IM. Shorter races like sprints might benefit from bricks. Twenty years ago we used to do this crazy brick workout of 5 x 1k run/ 5k bike repeats at just about redline pace (or 6x 1k/5k, depending on if you were going thru a divorce and really angry that day) . We would be trashed afterwards and then go for beers and wings. I don't know if it made us any faster, lol. Ah, those were some good times!

I do these a lot at home (trainer/treadmill), but honestly it's more about fighting boredom for me. Sessions like 4x (20min bike, 10min run). It helps keep you engaged in higher intensity, knowing that the light at the end of the tunnel is closer.