I don't see the point of buying a DX 100x probe. Perfomance will suck for low level signals, and I wouldn't trust it with anywhere near 1200 V.
Brand name (i.e. HP/Agilent, Lecroy, Tektronix, probably recent PMK designs) usually have a better signal integrity (eg. dielectric absorption and voltage coefficient in the input cap), less loading, better durability, more flexible cable, better access to tiny circuits (hello cheap probe makers, please start cloning thirty year old brand-name probes instead of forty year old ones, most of us don't use tons of 1 W resistors and tubes anymore).
That said, the cheaper brands are likely to work just fine for hobbyist applications with low bandwidth (< 300 MHz or so) scopes. Just don't expect them to last for years of serious use, most of them won't.
You can sometimes find cheap Tek probes on eBay, though you have to make sure you get the essential accessories (at least ground lead and grabber hook). Pay attention to attenuation (10x is by far the most versatile), compensation range (should include the input capacitance of your scope) and bandwidth (preferably at least 100 MHz).
Probes tend to be relatively more expensive than scopes (maybe 10% instead of 1% of the original price) mainly due to supply and demand. Probes are frequently thrown away by surplus companies to be sold for scrap, or tend to get lost or damaged much more often than the scope.
100x probes are not really intended for looking at high voltages,but rather as a 'Cheap & dirty" alternative to an active probe for looking at high impedance circuits where the 10MOhms of a x10 would adversely affect the circuit operation.
I was adjusting a Sony Picture monitor,where the book advised the use of an active probe for this reason.
"Nonsense!" said I,and tried a x10-----well,Sony were right!
I asked the boss for an active probe,& after he finished rolling on the floor laughing,he suggested somewhat forcefully,that I find an alternative way to provide the required high Z input on the 'scope.
A x100 probe from RS Components was the answer,although the signal was a lot fuzzier than with the x10,it was now possible to adjust it correctly.
Tektronix probes don't always fail in the same manner,& I have assembled probes using various "broken" units assigned to the bin.
I call them my Frankenstein probes!
"Time is money" in most workshops,& sometimes even expensive probes which may need a minor repair are put to one side & forgotten in the rush to complete the customer's jobs,so if you are lucky enough to find a bundle of Electronic junk from a workshop for sale somewhere ,you may find some Tek or HP probes in amongst the other bits.
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