You are right to pursue the details, and there is a "gotcha" in that Atolla device. Then there's another of less importance in the adapter on eBay.
The Atolla USB Hub has 7 regular USB3 ports, plus a special high-current charging port. EACH standard USB3 port CAN supply up t0 0.9 A current per the USB3 specs, BUT that can NOT be done for ALL of the ports simultaneously. The limit certainly is in the power supply module - it can only deliver up to 3.0 A max to the Hub. So, if you were using devices that actually pull the 0.9 A max for each device, you could only use up to three of them simultaneously. And of course, IF you were trying to use the special charging port to charge something else at its max 2.4 A output, you'd have less than the 0.9 A available at ONE USB3 standard port. This is a common habit in the design of USB3 powered Hubs - the power supply module is not able to supply ALL of the ports at max current simultaneously. The design concept depends on two factors: (a) you won't try to use all ports simultaneously, anyway; and, (b) even if you do, some of the devices (e.g., a mouse) will require much less that the max, so it will work most of the time. For this particular Hub, they make it easier for you to manage this by using a separate switch for each standard USB3 port so you can disconnect unused devices without having to unplug them.
For your purposes in using it with 2½" laptop-style hard drives via those adapters from eBay, you MAY not have a problem. Note that the adapter specifies that it can only be used with 2½" drives, and not the 3½" larger units for desktop machines. That is because the 3½" drive design uses BOTH +12 VDC and +5 VDC power connections, and there is no +12 VDC supply available through a USB3 connection. Among 2½" drives designed for use in laptops, MOST can work with up to 0.9 A at 5 VDC, but that is not ALWAYS the case. Note that the adapter write-up says you plug in the thicker USB3 cable to a USB3 port to get that much power AND use the high-speed data transfer ability of USB3. THEN IF your device still is not getting enough power, you can plug the smaller cable into a different USB port to get more power. It does not specify whether that port should be USB2 or USB3, but that really does not matter. SO, if the HDD units you plan to use can EACH work within the 0.9A max current limit of a single USB3 port, then for each HDD you would only need to use an adapter with the ONE thicker cable plugged into ONE USB3 port of the Hub, and it would handle that two-port load easily with the power module supplied. You really would need to find the specs for the 2½" drives you plan to use to verify this will work.
Your alternative, IF you believe you need more than 3.0 A max current for your purpose, would be to buy a different Hub that has a more powerful power module supplied with it. That CAN get tricky to read the specs. Unlike the particular Hub you linked to, many Hubs come with power modules that output 12 VDC to the Hub, and then the Hub converts to 5 VDC. So the power spec of the module is in WATTS usually (sometimes in A at 12 VDC), and you have to assume that most of those Watts will be available from the Hub's USB3 ports at 5 VDC, with an A rating reached by calculation. For example, if a Hub comes with a power module that puts out 12 VDC at up to 50W (4.17A), then the Hub can dispense that 50 W at 5 VDC, which comes out to max 10A in total for all the Hub's ports. For examples,
https://www.amazon.co.uk/dp/B00P115F4E/ref=twister_B0797F7WB3?_encoding=UTF8&th=1
is a 7-port powered USB3 Hub including a power module outputting 12 VDC at 2.5A at a price similar to the Atolla one. That means 30 W, so at 5 VDC it can supply up to 6 A to its seven ports, almost up to the 0.9 A max per port - maybe 1 port short.
https://www.amazon.co.uk/Anker®-Pow...sprefix=USB3+powered+hub,computers,340&sr=1-3
is a heavier unit for more money. It has 7 USB3 ports plus 3 charging ports, and a power module of 12 V, 5 A (60 W) output, so that's 12 A max available at 5 VDC, well able to supply the 0.9 A per port to all 7 USB3 ports PLUS spare power for the charging ports simultaneously.
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