Hi I don't own a Z so I can't compare.
The 1052e performs per its data sheet and what bugs it had or remains are not critical, they don't impact measuring capabilities; e.g. my unit may lock up if I hot swap a USB drive when triggering, the rotary encoders sometimes get too sensitive, type issues.
The c2008-2009 1000e has had time to mature. But even on initial release there were no critical bugs and brought Rigol's fame for its price performance. A variant of the 1000e series was rebadged for Agilent with the Rigol version having slightly more features, such as memory.
Instek as a company makes reliable devices [I've used them off/on for 30+ years] but they cost more and have less features for price, if you compare spec sheets. But it lives up to its spec sheet and its quality is consistent.
The 1.5 year old GDS 2000E series had bugs on release but none critical, you can read of the genesis of issues in eevblog forum reviews. The lower end GDS 1000B series is ~ 1 yr old and had no critical bugs, actually no bugs with my unit OOB and with current firmware. Because of the new technology used in 2000E and 1000B models, they are lower priced too to come close to the price performance of Rigol equivalent models, but with Instek reputation.
I suggest you get a scope from a local dealer, so you can test and exchange whichever until one works for you. What we see in eevblog's international forum is take home prices for models as well as availability vary with country. If you buy mail order international you could save but if things go wrong and its warranty not honored locally, it can cost a lot to ship back internationally.
Last cautious words: over the years of reading eevblog forum chatter, the quality control of Rigol has taken a step down in entry level devices of its product line: the Z, the 1000e series [ newer production] and the DP 832 PSU, to name a few. So test it thoroughly after receipt within the window you can return it to the dealership for an exchange.
Thanks for your helpful reply. One question on the below comment:
I have both a 1052e and a newer GDS 1054B with all channels identical in spec, both for measurement readings and function; I need them that way and I paid for that performance.
Is the (older, 2ch) Rigol 1052e a better, more accurate or more reliable piece than the 1054z?
I guess the same question for the Instek. I went with the 1054z because it seemed like it was getting lot of love on this forum. Also I liked that I got it through an Australian Distributer. I was also looking at Hantek, Siglent and USB Picoscope models. I don't need 4 channels, or fast speeds.