No, that 3-in-1 adapter will not drive multiple monitors.
What you need is either a system that combines 2 monitors, or a system that chains them. While DisplayPort allows for daisy-chaining displays, this only works on supported hardware. This means your monitors need to both have two DisplayPort connectors and official support from the vendor and inside in the chipset to make this work.
I believe that you aren't going to buy two expensive chain-able monitors since, well, you don't want to buy an expensive adapter ;-) The next stop would be stuff like Matrox's DualHead2Go. That is a device that allows 2 displays to be connected to a computer as one big display. http://www.matrox.com/graphics/en/products/gxm/dh2go/digital_se/
It does cost quite some money, so it might be in your category of 'expensive adapters'...
The problem with your question is that it is rather specific. It's a niche that most people don't even know about, and not a lot of sales or development is happening there. While it could probably be done cheaper, there simply aren't a lot of options here.
Just remember: one video port can only ever drive 1 display, unless it's a daisy chained display port system or a device that turns 2 screens into 1 big virtual screen for the video port. There is no cheap 2-in-1 adapter to make this happen.
Small addition: you might be able to solve your problem with a USB DisplayLink adapter if you do not need 3D video or accelerated 2D video. It's a video card with a USB connector on one end and a video port on the other. It won't be fast or high-performance, but if you simply want more desktop space, it might work for you. You would end up with one of these: http://www.displaylink.com/shop/adapters
USB Type-C is a specification for a plug connector. Thunderbolt is a specification for a transfer protocol.
The original Thunderbolt, in mockups prior to its final specification, showed a USB Type-A connector being used. The USB Implementers Forum refused to allow the USB Type-A specification to be used as a combination port, so the Mini DisplayPort connector was used instead. Thunderbolt 2 used the same connector.
The link from the Wikipedia article you linked, to "Thunderbolt Alternate Mode" (being an alternate from a USB transfer specification), explains that Thunderbolt 3 uses USB Type-C connectors.
The port is not masquerading as anything: Because both Thunderbolt 3 and USB Type-C devices use the USB Type-C connector, all devices that have USB Type-C connectors and that have macOS drivers, or that can operate using drivers built into macOS, are compatible with the port, as are all Thunderbolt 3 devices (ditto regarding the drivers). Thunderbolt 1/2 devices are compatible through use of an adapter, as are USB devices that have a Type-A, Type-B, Micro-A, Micro-B, or Mini-B connector.
Best Answer
You gotta love the heightened level of complexity that simplifying things down to one connector has made things. Let's sort it out....
USB-C is the connector type. It's the physical interface specification just as USB-A, USB-B, USB-Micro, USB-Mini are all physical connectors. It's not a USB port, nor is it a Thunderbolt port.
USB 3.0/3.1 is the USB specification and port type. It sets the standard for how USB will communicate on your machine. It's backward compatible with USB 2.0, 1.1, and 1.0
Thunderbolt 3 is the Thunderbolt specification that supplies DisplayPort, PCIe, USB 3.0 and power. It's backward compatible with Thunderbolt 2 and 1. Thunderbolt 3 utilizes the USB-C interface and Thunderbolt 1/2 utilize a mini DisplayPort interface connector.
Daisy Chaining - Thunderbolt can be daisy chained, while DisplayPort cannot. Usually, displays are last in the Thunderbolt chain.
As for the Macs...
MacBook Pros from 2016 onward have 2 or 4 Thunderbolt ports that utilize USB-C interfaces
MacBooks have USB 3.1 ports with DisplayPort support that utilize USB-C interfaces.
So, when you are picking your adapter, you have to determine what port you have on your machine first. Then you pick the physical inteface type that works for you.
For example if you have a MacBook, you will have a USB port with DisplayPort support on a USB-C interface. This means you can use a USB to DVI/HDMI/DisplayPort adapter or you can use a USB-C DisplayPort to DisplayPort cable. What you can't use is a Thunderbolt cable/adapter
If you have a MacBook, you have a few more options because of the inclusion of Thunderbolt.
As for the iMac... Thunderbolt is Thunderbolt. It doesn't change from MacBook to iMac to PC. A Thunderbolt adapter for the MacBook Pro will work on an iMac because, after all, an iMac is a MacBook Pro in a different form factor.