spacedesk and Duet Display

I found that I could install spacedesk, a well-known monitoring application, on my 4th generation iPad, which was sleeping at home, so I started using it as a second monitor for my mini PC. However, the 4th generation iPad, which is considerably slower than the latest models, in addition to the WIFI connection, causes a certain amount of display delay, and the mouse and other functions are too slow to be of practical use.
After some research, I found that Duet Display, which can be used to display a monitor using a lightning cable, can also be installed on a 4th generation iPad with iOS 10.3. This is a paid app, but I decided to purchase it this time because it seems to be useful in various situations.
When I actually tried it, I found it to be quite comfortable and almost as good as a regular monitor. The only problem is that the MINISFORUM UM350 is a mini PC and is small, so I sometimes want to use it by moving it around the room. It would be nice to be able to use it as a monitor in such cases, but Duet Display can only be connected after starting up the computer and logging in. spacedesk has an option to start without logging in 40 seconds after computer startup, so spacedesk can be used as a first monitor, but Duet Display only can't be logged in when computer starts up, so Duet Display can only be used as a second monitor. But since I only have one iPad (lol), I am pondering what combination to use.

Reuse old iPad as a Monitor

I bought a mini-computer as my second home physical computer and have been playing around with it, but I still want two screens (lol). When I was mainly using a notebook computer, a dynabook N40, I naturally had two screens: a notebook monitor plus an external monitor (a TV, though). The mini PC is a desktop, even though it is a mini, so of course it does not come with a monitor. The MINISFORUM UM350 seems to support Display Port and Type-C output in addition to HDMI output, so it can output up to three screens simply by connecting it.
My current desk at home is not very spacious, so the Toshiba Regza I use as a monitor is also positioned so that it is somehow outside the desk with a gas pressure arm , so I was looking for something portable and space-saving to buy another monitor, but then I remembered I have an old iPad at home. The iPad I have at home is what is called a fourth generation , which was released in 2012. It is not so old from the point of view of a Linux user like me (:-o), but since iOS only supports up to 10.3, most of the apps no longer work on it (;~s). I had to use a technic to install once on a relatively newer model with my Apple ID and then put the older version of the app on my iPad. But even so, most of the apps stopped working except Safari.
I did not expect much from such a situation, but it turns out that spacedesk, a well-known monitoring app, runs on iOS 10.3 as well! So the 4th generation iPad has started its second life as a monitor (lol).