MTD filing

Nope

As Blackfrier said, no you don't need to specify which MTD software you will use for each client when signing up for MTD.

What you will need to do is grant authority to your chosen software so it can communicate with HMRC. You do this within the software.

You can even grant authority to multiple MTD software solutions for a single client with no drawback. For example, you could grant authority to Sage and also Easy MTD VAT (https://easymtdvat.com) for the same client.

You may wonder why you would want to grant authority to multiple software solutions... As some on here have realised, having another MTD solution at hand is a good way to determine whether an MTD related issue (such as being unable to view obligations or submit a VAT return) is due to the software or the HMRC MTD system. This is particularly significant while MTD and associated software is in its infancy and the likelihood of problems arising is more likely.

If you are running an ASA you can have your ASA authorised for one or more different MTD services and the client can also have one or more different MTD services.

Hence if your client uses say Sage, they can authorise on Sage.

You could,however, decide to also authorise easy MTD and/or vat direct so you can monitor what is happening for your client.

What is particularly helpful is that you can use a system which manages multiple legal entities (potentially with multiple authorisation routes) to monitor clients more generally.

The only danger of this is hitting rate limits on the HMRC servers.

It is important to note that there are multiple MTD systems that operate in different areas. Hence you can supervise say Customs, Trusts, VAT, SA etc all from one system.

Much that you probably wouldn't do Customs or Lisa together with the others.