Just out of curiosity and for the fun of it, this past spring I collected seed from an F1 hybrid daikon radish and planted 5' each of both the OP and the F1 seed side by side. Boy, the test sure demonstrates the difference between an F1 and the collected seed! Here's one of each that I pulled ten days ago with the hybrid seed on the right, the OP on the left. Please ignore the turnips at the bottom.

 

Today I pulled another of each now that they've gotten bigger. The OP radish, now 1 lb 8 oz, has developed deep fluting on the sides and this one has grown a lot more squatty in shape than the previous OP.

 

I've learned that if I let the OP get this big it will get pithy in the middle. Gotta use them when they're smaller. I've not experienced that with the hybrid of this size. The OP also has a pretty thick skin to peel off which is a waste while the F1 skin is a lot thinner.

 

If you look closely at the the F1 that I pulled today at 1 lb 10oz you can see slight fluting on the sides as a result of it's lineage.



The original hybrid seed pack was bought in a Korean grocery and the writing is all in Korean so I can't read the name or anything else. The photo on the front is true to what I've grown for three years now so I'll stick to the hybrid for now. Meanwhile I will look for an OP daikon that looks and performs as well as the hybrid so that I can collect my own good seed.

That is really cool @GoDawgs . So interesting that fluted traits and even thick skin would be popping right out in the F2 from a high quality hybrid.

I had a Blues napa cabbage F1 in a pot from my winter grow last year, and it happened to bolt after I stuck it outdoors, at a time there was no other B. rapa to cross with so I let it set seed to see if it would self. I ended up with a couple hundred seeds and just started some recently. They look pretty uniform so far, so I'm really wondering what kind of differences will show up down the line. Kind of hoping both parents were similar for the important traits.

Kitazawa Seed carries quite a number of daikon with a few being OP. You'll need to check both radish pages.

Baker's aka Rare Seeds sells Minowase daikon which is not a hybrid. It's pretty good. I prefer Japanese daikon, the Korean ones are squatty and can get pithy as @GoDawgs mentioned.

I've grown Minowase and still have seeds in the freezer. It's great for fall planting; nice and mild. But despite catalog claims that it's great for summer planting I find that here it always turns too hot for my taste.

There's a Kitazawa catalog here and I checked out the radishes yesterday. They had the description for one of those I bought at the Korean grocery where the only thing in English was the variety name "Cheong Du" so now I have that info. They also have other Korean radishes that are long and not squatty and I was considering one. I see they've changed their shipping charges since last year when it was $9.00 for 1-18 packets. Now it's a flat $4.50 for orders under 11 oz of seed. That's a good thing. My penny-pinching nature still rebels at paying freight for one packet of seed so unless I find a few more things later today, I'll pass.

There are daikon varieties out there bred specifically for the hotter summer months but unfortunately they are not available here, or maybe I've just not seen any. The ones I've grown in the past were all hybrids. If I ever get to go on a trip to Japan next spring I'll be on the lookout for some @GoDawgs.

@GoDawgs actually I did find a summer daikon, Minowase daikon, & it's available from Baker's & Kitazawa. Curiously, I happened upon Walmart that also sells Kitazawa seeds(not all, but many) for the same price AND free shipping even for 1single pack! Minowase is on their site. I didn't check for the Korean variety so please do so.
Kitazawa Co. has an announcement on their site stating that they are allowing another company, True Leaf Market, to take over some of their operations. So perhaps that is why we can buy their seeds on walmart.com also. I was surprised to find shiso there, the Aoba variety, then noticed the Kitazawa logo on the page. Strangely shiso is no longer available on Kitazawa's site so I'm wondering if I'm getting older seeds. But with free shipping I don't mind, some seeds are bound to sprout & I'll save my own for the future.