Is this accessory kit a good addition to this telescope?

It never hurts to have a variety of eyepieces.  Of course, these don't have the BEST optics, but for the average sky watcher, they'll be fine.

Personally I wouldn't.  These eyepiece set are attractive to beginners since on the surface they represent a convenient and nicely packaged bundle that you can buy without properly considering what is in them.  In practice however, you don't need so many eyepieces and you wnt different things at different powers.

Looking at this set, firstly ignore the filters.  Coloured filters are cheap - you can get an equivalent set for perhaps $25.  They do come in useful at times but the effects are much more subtle than you may imagine.  I'd say those are something to consider later.  The one filter you do want - a Moon filter - is not included anyway.

Looking at the eyepeices the 7.5mm does not really add anything - it is too close in power to the 6.4mm and even the 10mm to make any significant difference.  Additionally, these are Plossls which have poor eye relief at short focal lengths.  I regard Plossls under 10mm as unusable, and I'd prefer a different optical design for the 10mm too.

My preference would be to select a couple of _good_ eyepeices and extend the range in the future.   A reasonable EP in the 15-18mm range would be my first port of call, followed by a higher power EP of 8-10mm or so.  I wouldn't go for a low power EP at this point since the 25mm that comes with the scope gives 48x, already quite low power.  If you want specific recommendations, I'd start with the high power one - probably a 9mm Meade series 5000, an 8mm Celestron X-Cel (good general purpose EPs) or a 9mm Baader Genuine Ortho (more of a specialist planetary EP).  Splitting the difference between that and the 25mm indicates you what the other EP to be in the 15-16mm range and a Plossl will be fine at that focal length - the Orion Sirius will be fine.

One final recommendation - don't forget a good collimator.  Forget any "Our scopes are collimated at the factory" statements sicne the scope will lose collimation in transit, and a poor collimation will impact the performance of your scope far more than an average quality eyepiece.  A laser collimator is the best option for beginners: while it is not the most accurate method it is by far the easiest for beginners, which translates in to it actually being done rather than forgotten about.