Do you think it will be successful to generate the keywords with site-service? I advice you to ask for the help the marketing services for successful ASO. ASO requires high quality, because it's the same as SEO for the sites. Crappy SEO will ruin your site. So, you can buy ASO in the service. Your ASO is icon, keywords, video and description and the full package provide everything that I described.
I have recently ordered ASO at Mopeak (app installs provider). They have New Year discount now. I really did not expected to get so high quality screenshots, and really effective description with the keyword for my app.
Okay, I doubt you will like my advice but I will still write it anyway. First of all, I am a developer that recently got OBSESSED with ASO. I do not plan to ever pay any ASO company. I instead run my own experiments and I would write more details about these later. Note that all my experiments were performed on Google Playstore.
So what I noticed is that the "Search Volume" data that these services show you are not accurate. Think about it (How can it be accurate). These data are not publicly available.
The most inaccurate metric, however, is the competition metric. When you see "Competition", users naturally assume it determines how easily you will be able to rank for that keyword, however, it is misleading. The competition simply says how measures how difficult it is to "BID FOR THAT KEYWORD AS AN ADVERTISER".
Now the best way to find high volume keywords would be to use Playstore autosuggest feature. Very simple and VERY VERY effective. Playstore will only suggest keywords that are popular. And the more it suggests, the more likely people click on it. However, if you search for some of the keywords that these companies claim to have "high volume", you will realize that Playstore does not even suggest them at all.