you're right about more in-depth information on plugins, I have a planned feature when holding right click over a plugin will give a box of expanded information about it. another tutorial level may also be a good idea.
here is what the plugins you described do:
Word Combo: typing out the word and then entering it will give you an amount of score. doing words back to back will increase this score multiplicatively, hence the "combo" part. the blue bar on the plugin indicates how long you have left to input the word before the combo expires.
Line Duplicator: this will automatically duplicate a percentage of every single line you send, accruing on a counter and then giving you the listed amount once the yellow bar runs out. what you described is a known bug with the plugin where it will sometimes not work when you buy the plugin under specific circumstances. this will be fixed in the next update.
thank you for your feedback!