[Merlin66 (Ken)]

Jim,
I've been a PST user for the past ten years (See below) and it was a game changer when initially launched in 2003 - it brought the opportunity of observing the solar disk chromosphere to the amateur for the first time.
It was designed and sold as a visual instrument. This restriction still stays with us today. Over the years the PST hasn't really changed...Ideal as an introduction to Ha solar and can, just, be modified (cutting down the eyepiece holder!!) or used with a low power barlow to achieve imaging capability.
The internal "heart" of the PST is the etalon which is 28mm diameter.
To pull more resolution and performance from the PST it has been the subject of more mods than any other scope!
I actively worked with amateurs in the UK to refine and understand the necessary hardware and construction of a successful PST mod.
There are Stage 0.5, Stage 1 and Stage 2 mods - usually using a larger aperture (up to 150mm) "donor" OTA.
OK so much for the PST - some critics say the design - gold tube/ black box is dated and should be upgraded......

Andy Lunt, son of David Lunt who designed the optics for the PST left Coronado/ Meade and set up his own business (2008) in competition - Lunt Solar telescopes.
The range of Lunt Ha solar scopes is impressive - from the 50mm "base" (the original 35mm - to compete head on with the PST was dropped) to a eye watering 150mm version!
He also introduced "pressure tuning" to the etalon assembly - this is said to give a more even field of view - a "larger sweet spot" - Hmmm

Most of the larger solar Ha telescope have reduced sized internal etalons (these are the very expensive parts!!!) and the etalon used in the Lunt 50 is very similar to that in the PST.
The Lunt design however took into account the growing popularity of solar imaging and it came with a conventional focuser to allow easier camera connection.
In "Imaging Sunlight" I present a comprehensive discussion (p13-18, p38-44) on current available solar telescopes and associated filters.

Summary
The 40mm PST is designed for visual but with work can be used for imaging
The bandwidth is designed to be <1A (usually around 0.7-0.8)
The etalon is tilt tuned for wavelength with some "sweet spot" effect.

The Lunt 50 has a slightly larger aperture and should (?) give marginally better surface resolution.
It is fitted with a focuser which allows fitment of cameras.
The bandwidth is the same as the PST
The etalon can be pressure tuned to "improve" the "sweet spot" effect.
Hope this helps