I have used Mozley Table. It is very fast and within a few minutes heavy minerals get separated from the light minerals. For zircon-rich rocks like granites and sedimentary rocks it worked fine. You can adjust the tilt and RPM of the tray. Also there are V- and U-shaped trays for different size fractions. The end knock action of the tray is very important for effective separation of heavies.

I used a Gemini table quite a lot in grad school; it worked fine but required quite a bit of upkeep and monitoring to make sure your heavy minerals aren't lost in one way or another. We routinely had issues with water flowing too fast or not fast enough; I think a lot of this had to do with the buildup of scale (from hard water). More recently I've used a Wilfley, and was pretty happy with how easy that was to use, but again it seemed as though there was quite a bit of upkeep associated with it. For what it's worth, I was borrowing someone else's Wilfley and didn't have much control over how others were using it and what it was being used for - so maintenance was beyond my control. I think I preferred the ease of the Wilfley compared to the Gemini.

You may consider having JCR Zircon Concentrating Table from Jasper Canyon Research. It is specially designed for zircon recovery and they claim about 80% zircon recovery.

I have used a Gemeni Table GT250 and with care to set it up correctly it works very well recovering HM down to 50 micron readily, some a lot smaller but I dont know the recovery curves there. There is published info on recovery curves which in a lab should be readily achievable. The water set up is critical and so is the correct close sizing of the HM you are separating. split your feed into a series of sizes not just a - 1.2 mm feed. Best to play around with some concentrates that are not critical to get it set up well to start with and get the water settings right. The 3 metre gravity fed head for the table water is very important so dont try to use mains pressure on a low setting.

Thoroughly recommend a Gemeni table and they make a lab sized one the GT60. https://mineraltechnologies.com/images/stories/virtuemart/product/MT-DS-014%20-%20Gemeni%20Tables%20Data%20Sheet.pdf

Water supply must be clean and worth flushing the water manifold after every days use to get rid of any silt etc that may be in your water supply, easy to do with one plug to undo.

I have used Loc 50 and Loc 500 for separation of the heavies at the Mineral Separation Laboratory of VU University Amsterdam. I found the devices are very efficient. You can check their website for more information: https://science.vu.nl/en/research/earth-sciences/laboratories/mineral-separationl-laboratory/loc500.aspx

We use the Wilfley Laboratory Unit (albeit an older model) for separating out zircon and heavy minerals before further processing, it's great bit of kit for quick mineral extraction. An added bonus is that the table it is quite high volume so can be useful if attempting to separate from zircon-poor rocks where more material needs to be processed.

http://www.holmanwilfley.co.uk/products/

Looking at the type of research you do (dust, Loess) you are likely to deal with the smallest of zircons?!?!? The Wilfley table may lead to dust-sized zircon overwash if your rate of water is too high. The Gemini table can be set up so that zircon (the >100 um fraction) stays on the table and you can use a pipette to "suck up" the residual zircon. It may still be likely that some finer zircon flows off the table. The Jasper Canyon Research zircon table is designed so that zircon stays on the table and is collected by pipette. I just purchased one, but have yet to try it because of COVID19 restrictions. It is not a cheaper option but might be more effective. I would maybe ask the vendors to complete a trial sample on each system and see what results they give you.