I have no idea what those services are. But 1) You should always build your own list. 2) If you want something "easy" then just pay for a solo ad in a publication in your niche. If you sell blue widgets, find a blue widgets newsletter that sells solo ad space.
Edit: Ok, now I see one of the companies you posted is a safelist. Meaning unless you target other people looking to make money online, it's probably a waste of time. You give your email address and agree to receive emails from other people who have signed up for the same thing that you did.
From the FAQ:
"You agree to receive emails to your list email address from other list members of the service.You can expect about 15 messages per day."
I used on of these type of companies early on, when I uploaded the list to my provider (constant contact) they promptly shut me down until I did an interview with them. After the interview I removed those from my provider and created a new account with a different provider, I slowly added them in in batches of 500 over a couple months. I thought I was pretty slick to "beat the system". When I ran my campaign, I was absolutely flooded with emails and calls nailing me for spamming them. People were furious. So, hard lesson learned and now I have a large organically grown list which works wonderfully. Bottom line is there are no shortcuts.
So may be email marketing works better than people think.
Email marketing is about as effective as unsolicited snail mail or phone calls. People are flooded with so many solicitations, I think it is safe to say the 99% end up trashed. Why do you think opt-out sites and do not calls lists are so popular.
The only effective way to do it without angering a lot of people is create your own campaign from people who sign up. As mentioned, there are no short cuts.
I think it will probably work, if you're willing to shotgun ridiculous amount of people, and tick off most of them to get a few sales. Most people aren't willing to do that, so it's not very popular with legit businesses.
I've gotten spam from some businesses every other day for years. Legit businesses that actually put their address out and everything. I'm sometimes tempted to call and ask them why they would possibly think I'd use somebody who has sent me spam every other day for years. But somebody must, otherwise they wouldn't do it.
Everytime I send a mailing I am positively surprised with results. But I take long long time to segment my receivers and spend lots of time on crafting the right message and subject. Once they open the email I sent them, a big part of them clicks or replies asking for a proper offer. It just takes way more time than sending one email to 50k subscribers when each of them is a different human with different needs.