The team at whizz advert was very helpful with their advice when it came time to set up our sms campaigns which included sending out texts from both mobile numbers (landline) plus email addresses through whatsapp too! They were always available by phone or via text message if needed. I can't comment about any downfalls but i would say that they could be more clear about what you need exactly before setting things up - so there weren't many surprises once everything had gone live. This service provided us good ROI and helped build traffic towards other pages/products within my website.