You can change your theme forth and back just in several clicks. Therefore, feel free to try EcomSolid. If you would like to uninstall it, go ahead, republish your previous theme and your layout will not be changed at all.
Even when you have already published your page using EcomSolid, you can still change back to your previous ones. There are 3 steps that you could follow if you want to be back with your previous theme:
Step 1: Login to your Shopify dashboard (through this link: your-store.myshopify.com/admin) and click on the “Themes” section.
Step 2: Once you get there, you can see your current theme and your theme library which includes a list of your previous themes. Choose the theme you want to get back to and click on the "Customize" button next to its name.
Step 3: If you want to publish your page in your chosen theme, click on the “Publish" button at the right top corner of your page. Shopify will ask you this question “Are you sure you want to publish Boundless? This will replace your current theme EcomSolid”. Click on the "Publish" button and you will get back to your previous theme.