Agnostic: you hit the nail on the head, it is instant gratification.
Pen turning: do all the different pins require different bushings?
Mostly yes, you need bushings for each "type" of pen kit. Bushings are usually the same size within the same "family" - there are different variations of the Slimline pens, but many of them use Slimline bushings (some do not!!). There are several pens in the Gatsby/Manhattan/Wallstreet II families from different vendors, but I believe they require the same bushings. If you buy a pen and a pencil kit with the same name, they will use the same bushings.
There are more advanced techniques, where you can measure the pen kit parts with a caliper and turn the pen blanks to match the individual pieces, but the bushings make it easier. Some people do both - using the bushings as guides, but measuring for that final perfect fit. I do that sometimes.
If you are interested in pen turning, check out https://www.penturners.org
. They also sell a $0.99 "IAP" app for iPhone and Android. It is slightly dated, but has bushing and tube dimensions for many kits from many vendors, and a drill bit fraction/decimal/metric converter that is really cool. I like the feature that shows you the nearest fraction (and error) to a given decimal dimension.
Each step of the pen making process has been a refinement for me. I have learned a lot along the way. How to drill, glue tubes, square the pen blank, and finish pens have all evolved over time as I gained more experience.
Best wishes and good luck! Post photos of your pens. :-)