If it's too dim for you without the protector, note that all of these add-ons will reduce brightness somewhat, so it'll be even dimmer with one.  If you're not happy with the screen brightness, and are within the 30 day return period, return the system and order one with a more suitable screen (note that this will likely mean ordering a higher-end model than an Inspiron, which are sold at the price-sensitive end of the market and built to that price point).  
Is there any experience about dim screen coated by matte screen protector? Would it be too dark? I have a Dell Precision 14 7420 2-in-1 laptop with a highly reflective dim display (250 nits). I think of Viascreens.comThank you!
250 nits display is highly reflective