Well, let me first preface this by saying "Better is relative".
In my personal opinion, I would probably save the money for some alternate forms of detection and recording (Multi-channel IR surveillance system).
But, if field detection is the way you wish to go then I would look at what differences in the two, and the value (at least in my opinion).
The primary difference in the two meters is the frequency of the energy which they sense. The Natural Tri-Frield is geared to both static and alternating fields. On the electrostatic energy side it can sense fields whether they are alternating (AC) or unchanging (static). Conversely the 100xe is geared to mostly AC electrostatic fields.
On the electromagnetic (EM) side, the two meters also have their subtle differences. The Natrual Tri-Field senses static magnetic fields and field fluctuations. These are changes in the magnetic field strength which happen very slowly, or the presence of field lines themselves. The down side to this is that those type of readings are prone to false positives. Conversely the 100xe reads alternating magnetic fields only. Its tuned into a range of 40Hz to 100khz. This is a range in which manifesting spirits are thought to resonate. Its less prone to false positive, but on other hand its more prone to picking up 60Hz readings from house wiring or power lines.
Finally the high frequency EMF area, what they call the 3rd field. Reality being that its really just an extension of the 2nd field but in a higher range. This is the area you'll often get false positives from any number of transmitter sources. Of course the post predominant false positive in this range is from Cellphones. Since lets face it we all carry those little EM factories in our pockets and tend to forget about them. Also any close radio stations, a pipe, picture frame, loose metal object which is tuned to the frequency of a nearby radio station could easily become and antenna amplify these frequencies. This is one reason I don't put a great deal of stock into any EM in the higher or 60Hz ranges.
Aside from my background in physics, I am also a licensed amateur radio (HAM) operator. So I know all about how easy it can be for objects to pick up signals in the EM range.
If I had to get one, of the two I would probably choose the Natural Tri-field. Other than the electrostatic side, I'm not so sure the 100xe would get you a significant improvement over what you have now for the cost.
Personal opinion only...
