People can really get hung up on "gain", "takeoff angle", and
"efficiency", using them as shorthand ways to decide how good or
effective an antenna is. But they aren't, in themselves, what count.
What counts is how strong a signal you're radiating in the direction you
want. (I'll talk about transmitting antennas and ignore the somewhat
different problems of receiving antennas in this discussion.) Let's take
a brief look at each of these and when it is and isn't important.

GAIN - It's often given as a single number for an antenna, as "this
antenna has a gain of . . .". Assuming that a reference is understood or
also otherwise specified, you can usually assume that the gain figure is
in the most favorable direction for the antenna. If the antenna is a
rotatable Yagi, where you can point the most favorable direction of the
antenna toward the person you're talking to, then the single gain figure
is meaningful. Otherwise, it's not. Who cares what the gain is in some
other direction? What you care about is what the gain is in the
direction you're communicating to. In general, an antenna with more gain
has narrower lobes. So if you're working people in all directions, the
odds are that the signal will be weaker with high gain fixed antenna
than it will with a lower gain antenna, since it's more likely to be in
an unfavorable direction for the antenna.

TAKEOFF ANGLE - This usually means the elevation angle at which the gain
is maximum. Just like the gain figure, it's meaningless unless you
happen to be communicating at that angle. An antenna with lower takeoff
angle can easily be, and often is, lousier for DX than one with a higher
takeoff angle -- if it has lower gain at both angles.

EFFICIENCY - This is a good comparative predictor of antenna
performance, but only if all else is equal. For example, improving the
ground system of a ground-mounted vertical will improve its efficiency,
but won't appreciably affect the pattern. So whatever direction you're
using to communicate, the signal will be better if the efficiency is
better. Likewise, reducing the conductor or capacitor loss of a small
loop antenna improves the efficiency but doesn't affect the pattern. So
it will improve your ability to communicate in whatever direction. But
the vee beam and rhombic are different critters. All else isn't equal
with these antennas when the efficiency changes. The resistors, as
others have pointed out, kill only one lobe and leave the other pretty
much alone. So if you're using only the one lobe for communicating, the
lowered efficiency doesn't matter a bit.

I don't know if the resistors in the Ten-Tec antenna also absorb some of
the power radiated from the front lobe. If so, then they do reduce the
antenna's effectiveness when communicating with that lobe. But it's an
easy antenna to model with any of the currently available programs
(except MININEC-based ones if it's less than about a fifth of a
wavelength high). Figure out what direction(s) you'll be communicating
in. Use a propagation program like W6ELProp to figure out about what
elevation angles will be important. Then model the antenna and look at
the pattern, not just the maximum gain or the takeoff angle, to see what
the gain is at the azimuth and elevation angles you'll be using. Model a
dipole or other reference antenna at the same height and compare it to
the antenna at the azimuth and elevation angles of interest. That will
tell you what you'll get when you replace one antenna with the other.
You might be surprised. At the very least, you'll learn a lot.

Roy Lewallen, W7EL