As John said above, the concepts and techniques for pen turning are all pretty straightforward.
In my opinion, the slimline style of kit, commonly recommended for beginners, is actually one of the more difficult, partly cuz of small diameter.
Also, the technique of mandrel turning with bushings, also commonly recommended for beginners, is more difficult for me than "turning between centers", or TBC. . I am not sure why that is, but I find TBC much better, using calipers to check the size frequently ... may sound harder but it's not.
Sometimes the difficulty with a particular kit comes from the way the instruction sheet is written .... some companies do a great job with their instructions and some do a very sketchy and inadequate job. . After you have done a few different kits you get to know the techniques and can often dispense with the instructions altogether. . But it is always best to read the instructions in case there are any little tricks to be aware of. . The order of doing things can sometimes be quite important.
You ask ... "Is it more difficult to achieve a smooth or clean blank to hardware seam/transition in some kits?"
My answer is that it is more difficult to achieve smooth/clean transitions if you use bushings as your guide .... but this need not be the case.
It just seems to me that with bushings as your guide you seem to feel compelled to "turn down to the bushings".
In my opinion, that is often not the best approach.
I like to measure my kit parts, use calipers, and try to turn my blanks just a few thou bigger than the hardware sizes.
For example, if my hardware size is 0.425", I will turn down to 0.430" or 0.432" .... that is, about 0.003" or 0.004" bigger ON THE RADIUS.
My reason is that I always follow the turning with some sanding, which further reduces the size a tiny bit.
Another reason is that, from an aesthetic point of view, a little bigger is MUCH better than a little smaller ... "smaller than hardware" looks bad.
So you can make your life easier and better by learning techniques. . But I don't generally go along with believing in the "difficulty of a kit" as such.
I have never understood why the slimline is a "beginner" kit .... IMHO it is not. . If anything, it is more difficult due to smaller diameter.
When you go to smaller diameter, a 0.001" error is a bigger percentage of the final result and that can show !
Another thing about bushings ... you should never "nick" them with your tools. . Once you do that, throw away the bushings ... they are useless.
Just my two cents worth, as they say !! ..... (but it's really worth more than two cents ...... LOL !!!

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