[Xiaomi Redmi 1S] ManSamVampire:
My opinion of AICP 13.1 after using it for 4+ months

Yes you can use it as your daily driver. It is a great ROM if you are ready to accept some bugs and missing features:-

Camera works only in the already-included camera app — LineageOS Snap. If you try to use the camera in any other app, it gives an error. (eg. WhatsApp says "Can't connect to camera")

Although the camera works in Snap, it doesn't mean that every feature works. You cannot take photos in HDR, some camera filters do not work and you can't record videos.

There are some frequent temporary problems with camera focus and camera flash. But they are usually solved by zooming in and zooming out, or restarting the camera app.

There is a lucky time ;) in the ROM in which the camera miraculously starts working in all apps (but the quality in LineageOS Snap is still the best) and this is the moment when Footej Camera can successfully record videos too. However, it cannot be predicted when this lucky phase occurs.

I've noticed that it usually occurs once every 8 or 10 reboots or so. Or it also occurs when the phone reboots after the camera mediaserver fails (which happens after you try to take a photo in HDR).

No data usage counting and mobile network settings are available; nor can you access this info from any other app because the ROM itself doesn't support this.

However if you need to modify access point settings, I had mentioned a workaround in an older post.

If you need to change the network type, then you can do it by launching Phone Testing from the dialer by entering the special code.

No "notification access" feature support.

No customisation options to change the function of hardware navigation buttons.

GPS performance is poor and the compass doesn't work in all apps.

However, if you don't need to navigate in Maps frequently, you don't need to worry, because if you just need to check location, then there are no issues because assisted GPS works perfectly especially when WiFi scanning is enabled.

There are some exoplayer problems because of which most of the times, you cannot play videos/GIFs in WhatsApp and other apps that use exoplayer. (Force stopping and reopening the concerned app temporarily solves the problem or you can simply use another video player that doesn't depend on exoplayer, to manually play the concerned file)

Also, there is a problem that you cannot zoom into photos in the Google Photos app because it crashes after zooming.

No let's come to the good points in the ROM:-

Stock Android with LineageOS and AICP additions

Performance is great and you can usually work with 4-5 apps minimised which is a great improvement over MIUI 9.

Battery life is much better than what you get in MIUI with stock kernel. I am getting about 12-14 hours of battery life (with about 2 hrs of screen time) using my ~5 year old battery (I am still using the battery that came originally with the phone when it was bought; never found the need to buy a new one). Your results may vary depending on the condition of your battery but I can say it will be definitely better than MIUI 8 and 9.

Low standby power usage - I lose only about 5-8 percent of battery during the time I sleep at night (when mobile data is off and WiFi is on.)

No heating issues during standby - In stock MIUI, when mobile data is left on and WiFi off, then the phone temperature rises considerably and battery also drops very quickly. But in this ROM, the phone gets very slightly warm and battery loss due to mobile data is not that drastic.

Important: Right from the first week of flashing the ROM, I am using the ROM with low ram config enabled, i.e. in Android Go mode. (This is not enabled by default.) So if you are not using Android Go mode, your performance and multitasking experience may vary.

I personally love using it as an Android Go phone because right from the instant I enabled it and rebooted the phone, the system's RAM usage considerably decreased (~60-80 MB) leaving more space for user apps. And also, there's not much to lose in Android Go – there is no split screen support, no tab previews and gestures in Chrome, no emoji search in Gboard Go etc. and I'm fine with all these limitations.

Tips:-

If you are using a quite old battery, it is better if you set the Battery Saver to trigger at 25% battery so that the critical battery level (10%) is pushed slightly far.

Enabling the battery saver really does great in reducing system power consumption (If you compare with MIUI, enabling the battery saver in MIUI had almost no effect on reducing the battery consumption of the device. )

Don't let the phone heat up too much as I personally feel that rise in temperature has a very big effect in bringing down the phone performance (At least in this ROM, it is the case.)

So, keep the phone in good ventilation and don't use very thick body covers as they obstruct exchange of air.

If you are using an old battery, I would suggest you to apply kernel mod to set max freq. of CPU at 1.5Ghz or 1.4Ghz otherwise the phone tends to freeze very often when the battery is low. That's because I feel that the old worn out battery cannot take the heavy CPU load.