I have one kid in Riedells; used to use 875s. Now 1900s. Also have one kid in Harlicks, used to be in Klings, both customs.
The Riedells are great if you have a Riedell foot. They will also do "basic" custom changes, but, they don't do full custom.
In terms of "Harlick" vs "Klingbeil" foot ... if you're going full custom, it really doesn't matter. My kid has weird feet; both boots fit perfectly, and I know others with custom boots from the same makers who have equally weird and very different feet that also are perfectly fitted.
In terms of the options: We got the same in both boots. Both have heel locks, extra padding, tongue "posts", roll tops to prevent "rub" at the top of the boot (successfully for both). Both are at the same stiffness level; we changed because of the Klingbeil possible bankruptcy. So, I do have two identical pairs of boots to compare.
In terms of cost, looking at buying now, the Harlicks would be cheaper as all of the features we want are standard whereas it seems that Kling would charge for some of them. We have had no problems with the Harlick insoles; I have however, recommended them to another skater who needs "real" orthotics as Harlicks does good work with those needs. Both are heavily padded in the ankle area; both heel locks are excellent, and work well. Both hold down a very very very narrow heel up to triple jumps and spins. Both fit perfectly.
Differences: I like the quality of the Harlick leather. It's elk, and it seems to wear better than the Klings, and it's a nicer sheen/texture (IMHO). Harlick have a higher heel (although you can change that with custom) which helped with jumps and spins, I think the Harlick heel height is closer to the Riedell height - Klings are flatter. The Harlicks look neater, IMHO, on the feet based on the cut - they are very traditional in style. The tongue hasn't had the same issues with twisting as we had with the Klings (even with the posts in regular use and careful usage). The Harlicks are harder to lace up; you have to seriously pull them up with the laces as otherwise the fit isn't as perfect as it might be. The leather in the soles seems to be holding up better under wear and tear and moisture ... maybe it's the way we have them sealed, though.
My kid also found the Harlicks far lighter than the Klings, which was great. We have a "sweaty feet" issue, and the Harlicks come with Clarino leather inside at no cost, which helps with moisture resistance. IIRC, Clarino leather is a Kling option, but, it used to cost extra ... don't know about now.
I've heard of many skaters locally who have had problems with Kling orders of late; wrong sizes and features, slow turnaround time. We are really rare ducks around here with Harlick: it's very unusual, so I can't comment. However, the boots were perfect fit out of the box, measured by local fitter. We are sticking with them for future skates without question.