Obviously I've not used that software, so it then comes down to what can be found out about the application before taking the plunge (or not) That's difficult to judge from just looking at a website (even if it's nice and shiny and/or hits the top of search engine lists!). Nice shiny websites require web development skills (not a good product to sell) and Search Engine optimisation is a big subject these days. The best I can do is advise you how to assess the developer and product.
Now - before going on I have to say that what I'm describing below is risks and assessment points I'd think about when considering any software. Not any indictment of this particular product (which may well be a perfect tool exactly and what you need).
Necessarily my assessment points are somewhat paranoid. You get that way working with IT security!
(a bit of a simplification but...) any software could do something other than the seller advertises - bundle unwanted code (adware/spyware/malware / steal info from your computer etc) so you need to develop some level of verifiable trust with the developer.
There’s also the assessment as to whether the software will actually work well enough to meet your goals, and if it does not, what recourse you have. In your case email migration is a complex task, many things could trip up a conversion process.
So what can we find out about this program/developer?…
Looking at the website - I see a few minor things that hint to me that English is not the vendors first language.
I did a lookup of the domain name - it is registered to a company Gladwev but to an individuals name, rooted in India. Nothing wrong with that, but there is not a lot to hint at where the dev is located on the site itself - you’d probably not have expected it to be India. The domain name hass been around a while - at least the developer is established.
Also looking at the website and the companies central website www.gladwevsoftware.com, I see reference to various awards. However what are these awards really? - it does not say (and certainly there is no way to verify the award from the organisation who made the award. Hmmmmmm….. To me that reduces trust.
I also did a quick search to see if I could find any reference (preferably verifiable) reports/recommendations from bona-fide users. For instance, I’d put more credibility in a post on a long running blog site discussing multiple subjects which just happens to mention this episode in the bloggers life, or in a post on a trusted forum by a long standing forum member with many varied posts to his name. I’d put negative credibility in a post (to lets say this thread) by a member who just joined and for whom it’s his first post (or has 15 post all of which say “use super converter-pro - it works great [and even makes my clothes come out of the washing machine whiter!]”). As I say I only did a quick search but didn't come up with anything - either positive, negative, or neutral.
If I had to throw a dart at offering advice - I’d say that maybe they are bigging up their product and possibly the size of his business a fraction more and in ways than I’m comfortable with - can you then trust the other claims about support etc?
On the plus side there is a trial version - If I read the limitations correctly, you can convert one folder.. I suppose it’s worth giving that a go, and maybe also engage with the exulted Expert Premium 24x7 support - see if it lives up to their claims. If you have the chance try converting several folders with varying types of content. Think some attachments, some emails with various languages/character sets, html content/rtf content etc.
In the same way as mentioned , you could also search the other products on the Gladwev website to see if you can gain any trustworthy information from other internet users. That would also be useful as really we are looking at the company as much as the individual product.
Obviously if you do choose to purchase, assess the security of the purchase process as you go and if possible pay by something like PayPal which abstracts your payment information away from the vendor.
Of course these same principles can also be applied to any other software you research as a result of this (or other) requirement.