Can I use the CyanogenMod Installer app to flash Cyanogenmod 11 in my htc explorer which is already rooted and a custom rom is installed, and I have a twrp recovery,so I want to know would there be any problem if I do that,please I need some suggestion...
No you can't. The CyanogenMod Installer app is only available for Supported devices, which can be found at the CyanogenMod Wiki.
For this device, you'd need to first unlock its bootloader, which I presume you've already done, since you say that you've already rooted, and have installed a custom ROM. Update to the latest version of TWRP recovery which can be found here (which supports installing KitKat), or you could also go for alternatives like Philz Touch recovery (found here), which I am currently using. Note that you need to use the latest version of recovery, as there are certain changes in how KitKat is installed, causing the installation to fail in older recoveries.
You'd need to manually flash the CyanogenMod 11 update, whose two variants can be found:
- Official CM11 thread (by galaxyfreak): http://forum.xda-developers.com/showthread.php?t=2535682
- Weekly CM11 builds (by me, aka thewisenerd): http://forum.xda-developers.com/showthread.php?t=2611381
As for the "problems" part of it, can't really say. Only Instagram is found to be buggy (with the uploaded pics, in black color (?)), and of course, Flappy Bird lags a bit (the solution to which probably lies in reverting some upstream changes, and/or the build.prop). I would really suggest that you take a backup of your current custom ROM, try CM11 (or any other KitKat ROM for that purpose), and restore your backup, if you feel it's not worth the update.
Also, do use Google, to find the answers for your queries first (and a topic that's directly related to a particular device, i.e. HTC Explorer, you'd have rather searched here). Its always probable that your questions' already been answered.
Note: As to why I'd say that you'd turn to XDA Developers, as because development for this device primarily takes place in the XDA Developers forum. That's why.