The best thing about them is that they provide me daily updates of my list as well its size which helps in making sure I don't waste time reaching out for dead people or prospects who have moved away from our business area/industry etc..
Their support team has also been really helpful when it comes down issues related their systems especially during big campaigns like Black Friday / Cyber Monday (bigger than other companies). There were times where we faced errors while uploading files but since then this issue seems resolved so far! Nothing much at all except nothing majorly negative either! You should give mountain top an opportunity if ever looking into buying leads online because there's no better option available right now compared what i've come across personally. They help us maintain quality contact database without wasting valuable resources by having someone do manual work over emailing back n forth between.