Hi,

I've moved some sites from Modern to Bootstrap and vice-versa (albeit not recently, although I don't think anything has changed). For what it's worth, my view is:

• Modern and Bootstrap, whilst not identical, share a lot of characteristics. 
• There are some differences – that's why they are separate themes – but these are mostly visual/cosmetic. 
• For nearly all sites, moving from one to the other won't result in any significant issues, but you may want to tweak your site after switching.
• There are a few minor features that are only easily available in one theme or the other - see the list below for the main ones.
• I think you'd probably only run into trickier issues if you've used your own css file to heavily modify the appearance of your site.

I've listed the main differences below - these may be where you'd need to adjust things to suit the new theme. So, off the top of my head, the differences are:

• Modern has an 'about us' drop-down at the top of the page which displays group description, contact information, social media links etc
• Modern's navigation menu only appears horizontally across the top of the pages, and 'clings' to the top as users scroll down the page (so is always visible). Bootstrap has a slightly wider range of options for navigation menu placement and appearance, but its menus don't 'cling'.
• Modern allows you to easily choose a custom main colour for the theme (so if there is a specific shade of purple that you're particularly attached to…). You can specify the main colour in Bootstrap, but not as easily.
• Bootstrap provides more 'out-of-the-box' looks – 18 as standard, each of which can be selected and tweaked on your 'themes option' page (admin > look & feel > themes > options). 
• Bootstrap allows you to display a banner image at the top of the page. This can be modified with additional html (to display a slogan or contact details, for example).
• Bootstrap allows you to easily hide the crumbtail shown at the top of the page.
• Bootstrap allows you to add raw html to the header and footer of the page (particularly useful if you need to add javascript for analytics or cookie consent etc to your page).

There'll certainly be further differences between the two, but hopefully these are the main ones.

I think Modern is a very clean-looking theme, but my personal preference is for Bootstrap – for me, it is the more flexible of the two  (both in the standard settings provided on the Voice 'theme options' page, and also if you are using your own css file to modify things).

The Voice system is quite forgiving about moving between themes, so if you try Bootstrap and don't like it, you can switch back to Modern (or the other way around). Perhaps choose a time when your site is likely to be quiet (like late evening, early morning, Sunday brunch etc) and try it out. If you are moving to Bootstrap, there are quite a number of options to explore, so you may want to allow some time to play.

There are couple of help pages with further details about the themes here:

• Modern
• Bootstrap

Hope this helps,

John