I've been using Boomerang for much longer than a year, that's just the longest option this allows me to choose. I use it every day and am still probably underutilizing its capabilities. With it I have been able to be on top of follow ups, handle emails when top of mind but make sure they go out at a more optimal time for response, and with Inbox Pause... Catching up after OOO has been so much easier.
I set it up within minutes. The google sheets integration is smooth. Sent out campaign to 300+ in one day with personalization and scheduling. The feature set is pretty expansive. Looking forward to use the Saleforce integration. If it works well, that would be epic! Very straightforward to use and measure success
Meanwhile I think an onboarding guide will really help after setting up the account. Somehow I missed it and had to spend a bit of time to understand how to setup my first campaign.
Used YAMM on and off for a few years now when a more personalised mail merge approach is required. Have used it on mailouts to several thousand people eg. for invites (all optin in case you were wondering).
The mail merging is great, the integration between sheets and Gmail is pretty straightforward and once you get into some of the dynamic stuff sheets can do, there's all sorts of ways of using it: custom links, attachments, event custom pre-filled forms.
It's pretty quick, too, even for sends with hundreds of email addresses. Downside is that you can get yourself in to trouble if you're not careful about making sure you're OK to send to those emails, especially when new stricter data protection rules are coming in across Europe and California. Make sure you've got permission to send and respect opt-outs!
Only niggle is that if I want to send multiple campaigns from the same spreadsheet, YAMM sometimes can't find the email addresses, even when following the instructions, but there's ways round this (duplicating the sheet), however it's sometimes useful to keep all the YAMM campaigns on a single sheet with different columns for each email sent.
Use YAMM for personal touch.
Use others eg. Mailchimp, etc for bulk emails.
In summary, excellent product, good support, well worth it.