900TVL Cameras? Good? Bad?

Well if these are on conventional DVR and NTSC standard then...

From Wiki

NTSC color encoding is used with the System M television signal, which consists of 29.97 interlaced frames of video per second. Each frame is composed of two fields, each consisting of 262.5 scan lines, for a total of 525 scan lines. 483 scan lines make up the visible raster. The remainder (the vertical blanking interval) are used for synchronization and vertical retrace. This blanking interval was originally designed to simply blank the receiver's CRT to allow for the simple analog circuits and slow vertical retrace of early TV receivers. However, some of these lines may now contain other data such as closed captioning and vertical interval timecode (VITC). In the complete raster (disregarding half lines due to interlacing) the even-numbered scan lines (every other line that would be even if counted in the video signal, e.g. {2,4,6,...,524}) are drawn in the first field, and the odd-numbered (every other line that would be odd if counted in the video signal, e.g. {1,3,5,...,525}) are drawn in the second field, to yield a flicker-free image at the field refresh frequency of approximately 59.94 Hertz (actually 60 Hz/1.001). For comparison, 576i systems such as PAL-B/G and SECAM use 625 lines (576 visible), and so have a higher vertical resolution, but a lower temporal resolution of 25 frames or 50 fields per second.

Of course this does not address the compression of video at all.

Joshua, "Lines of resolution" or "TVL" is not the same as scan lines. While NTSC analog is made up of 525 horizontal lines (two fields of 262-1/2 horizontal lines interlaced), which is what you are referring to, Lines of Resolution is the maximum number of individual vertical lines you can see on a square section of the screen where the width is equal to the full screen height (3:3 vs. 4:3) before they blur together.

NTSC is typically limited to approximately 500TVL though some "tricks" can extend that somewhat. 900TVL is not possible with either NTSC or PAL. Essentially, 960H technology requires special encoders (and monitors?) to take advantage of the additional resolution, although we tested one 960H camera with a 960H encoder and saw no resolution increase over 4SIF/D1.

Although I only tested one 960H camera (Vitek) with a 960H encoder, I didn't see any difference in resolution between it and a good 600TVL camera through a 4SIF or D1 encoder. Considering the limitations of analog, I wasn't surprised. Pixel counts mean little with analog once you reach approximately 500TVL.

And despite D1's supposed limitation of 720 horizontal resolution, it cannot capture the full resolution of even 470-480TVL analog cameras. That was proven in a series of encoder tests we performed last year. We tested Avigilon, Axis, Bosch, Sony, TKH, Verint, IndigoVision, Pelco Endura and Dallmeier encoders and not one of them was able to provide encoded resolution anywhere near what we obtain from 480TVL to 600+TVL analog cameras fed directly to Orion and ViewZ 19RTC monitors via a Pelco 9780 matrix. Not even close!

You guys like 900TVL? How about 1200!

And - it's anti-dazzle!

900TVL appears to be a marketing trick, like 700TVL and 800TVL before it. My understanding is that these work with conventional DVRs while magically increasing video quality even though the rest of the infrastructure (e.g., the analog encoder) does not support those higher TVLs.

My thoughts exactly. The weakest link theory.