It all depends on how you design your signal flow.
First and foremost, UA interfaces are top quality. Excellent preamps, super quiet, highly dependable. So, adding one certainly doesn’t hurt. For Mac users, the thunderbolt units are incredibly fast. Their plugins are also top class, some of the finest in the industry. They are highly valuable an hold a high resale value as well. Finally, they are vastly superior to Audient.
Now, if you are inputting your instrument signal into the MOD and processing it there already, then you may not need so much processing at the interface or computer stages. (Most UA plugins are for post-processing). So here is where you need to assess how much post-processing power you still need – mixing, normalising, etc. – and how much improvement over the final output mix and overall audio quality you need. For instance, MOTUs are nice and flexible, work well standalone, and are great quality for the money. But the effects are weak and the overall sound is quite dull. An Universal Audio interface really shines when you playback over the monitors.