I have the second one, and it gives abysmal results.
Here is perhaps another way of looking at this situation. There
is a scientific proverb that says:
-- Some things are easier to see than to measure.
-- Some things are easier to measure than to see.
Let me explain: Consider the chemistry demonstration that creates
a huge billowing colored flame, using a squirt bottle and a solvent
with some dissolved ions. It makes for an attention-grabbing demo,
but if you wanted to do serious spectroscopy you wouldn't do it
that way.
I put Teltron tubes in the same category. They are a flashy way of
showing that electrons exist, but if you really wanted to measure
something you wouldn't do it that way.\1\ To this way of thinking,
a Teltron tube should not be called "e/m apparatus"; perhaps a
better name would be "electron porn".
Reference:
\1\ T. D. Whyte, N. P. J. Rymills, and J. S. Willis,
"Measurement of e/m0 using Dunnington’s method—An experiment for advanced undergraduates"
American Journal of Physics 52, 706 (1984) http://dx.doi.org/10.1119/1.13574