Ive used cheap Union bottle dynamos, expensive Nordlicht ones and Shimano dynohubs.
There is a big difference between old-cheap and modern-quality bottle dynamos but just as important is the mounting bracket.
Clamp-on mounts are useless, they can't counter rotational forces well, they slip around under the spring load and get knocked into spokes. I have a seatstay braze-on tab on my touring bike and use the Nordlicht to power front and rear lamps. The braze-on and mount should be as short and stiff as possible to maximise grip. A rubber ring and Marathon tyres combine to give slip-free operation that does not cut up the tyre sidewall.
I use a dynohub on my daily commuter which is fantastic, especially with a modern Lumotec Fly IQ LED lamp. For touring, where I only use the light for short evening rides or in emergencies, the sidewall is a better option.
I have powered Lumotec and Hella lamps and they are both better than old 1970s Union ones. The Fly IQ with senso and standlight is much brighter.
When you make your own lamp unit, can you maximize the efficiency of the reflector like in dynamo headlamps? You only have 3w to play with so you cant spread it around ober the road but you do need some peripheral star pattern for safety.