Although I think that the price for Sketch is quite high for a plugin, it’s not so bad for an independent application. With that being said, if you do go for the standalone product, I highly recommend spending the little bit extra and getting the Home Deluxe license. Even if you don’t have a host photo editor that is compatible with Sketch now, you may end up buying or having access to one in the future. And, while it’s nice to have the option of creating these images in a standalone program, using them in conjunction with an application like Photoshop or Paint Shop Pro makes the process even easier.
A free 10-day trial of Sketch is available from AKVIS if you want to give the software a try before making the investment. If you do find that you like it, you may want to look into some of their other products as well since a substantial discount can be had when purchasing one of AKVIS’s bundled collections.