Verified answer

The other answers are right -- in theory.

But the centre channel is critical to enjoyment of movies in surround sound. Given the speakers you are looking at are pretty low end models I suggest it's much more important to have a good centre channel for home theatre that to worry about timbre matching (all speakers from the same family).

The speaker you are considering isn't a great centre speaker, so .... get the best dedicated centre channel speaker you can afford (a perfect opportunity to buy a used model ... you may find a $300 speaker cheap) and don't worry about whether it matches (other than aiming for the same impedance ... 4 or 8 ohms ... as the surrounds) since you will balance the sound levels when setting up the system.

As to mounting, there is actually a good argument (See link) for NOT mounting a MTM (mid-tweeter-mid) centre horizontally ... if you mount it vertically it is less likely to give irregular horizontal dispersion (the sound will be more or less equal over a wide horizontal range).

Ideally you want the speakers to match all around. The center speaker is just made horizontally for fit issues. The thing is that you want all speakers level at the center of the screen, which in most cases puts a speaker right in front of the TV. Now if you are using a front projector you should be good, as you can put it behind the screen.

Timbre' (how speakers sound alike) is important and you should use three pairs of speakers (gets you a 6.1 set up BTW) for best results. The pros use this kind of set up, so why not for you.

Have you listened to those speakers yet? Matching your center speaker to your L/R speaker helps to prevent movies from sounding unnatural. As a general rule about 60-70% of a movies sound track is generated from the center channel. You can use the exact same speaker for your L,C,and R, but make sure first that you enjoy the sound from those speakers.

Do not use any other speaker except another one of these for your center.

It is important that all 5 speakers match instead of having a special "center".

Often center speakers are constructed wider with 3 drivers in a "midrange-tweeter-midrange" setup known as "MTM". There is some acoustical theories that are behind this - but it has a very small effect for music, and it is questionable if the theories even apply for home theater sound.

So I echo answerToAll's advice: get 6 of these speakers and use one of them for a center.