Having tried many games on Steam Deck, I can confidently say that shooters are not as scary as poorly optimized strategy games for a joystick. So before buying, I had some concerns, but as it turned out - in vain. But let's break it down by criteria. 

I'm trying the early access version of the game and I think a lot will be fixed by release, although I didn't find anything critical. 

Graphics and performance

The game doesn't lag anywhere and runs very smoothly. I'm not a fan of measuring fps, so there won't be any here, and in Heroes, honestly, it's a meaningless metric. So only my feelings - the console's hardware handles the game at 5 out of 5 with all settings maxed out. 

Buttons and controls 

Here it's not entirely comfortable yet, more quick keys are needed in the default settings - for example, all buttons on the back panel are not assigned, although there are actions where they are really needed - for example, continue hero's path. There is a small button on the screen, but reaching it via the trackpad is not very convenient. 

It's comfortable to play both via the trackpad and via the joysticks. 

Informativeness 

I singled it out as a separate block, because there are many objects on the map, and it's not always convenient to look at them on small screens. Even though I played Heroes on different screens, for example on an HP Palm Pilot. 

But it turned out that everything is convenient and clear. At the beginning of the game, I had a complaint that it was not clear whether an object on the map was interactive or not. In Heroes 3, they stand out more, and I'm already used to where to click. But then in the settings I found the option to highlight all objects - this solves the problem. 

Does it drain the battery?

Many people don't consider this factor, but it's quite sad if the game drains the battery in 1.5 hours, and you still have three hours to fly. Here everything is fine with this. The game is not demanding on power consumption and the device lasts quite a long time - about 3-4 hours. It also depends on the display brightness settings, but here my brightness was almost at maximum, because the game's graphics are not yet optimal and you need to see all objects on the map well. 

Conclusion 

You can safely buy it and play on the go. I no longer see any critical issues, so I think you don't have to wait for the game to exit early access and can buy it now - it's quite playable on Steam Deck.