I'm not a HUGE fan of the Explore, but I admit that it's a robust and sturdy piece.
#Note: Find full B&O review list at the bottom.
If you're looking to get a truly portable Bang & Olufsen speaker; then the Explore and A1 are your only choices.
In summary, the A1 does sound noticeably better (especially in the bass department) than the Explore. I'd recommend getting the Explore over the A1 only if durability (waterproofing, scratch resistance, dust proofing) and/or longer battery life is crucial for your needs and desires.
In other words, unless you're going to use your new speaker during the extremes (climbing, diving, camping)... The answer is simple. Definitely get the A1.
The A1 also does come with a microphone, unlike the Explore.
Make sure to check out the Explore vs A1 comparison chart on bang-olufsen.com, too. It's very informative.
Now let’s take a closer look at them.
Sound Quality
The Beosound A1 performs spectacularly when it comes to sound quality and performance. Although they're similar in size with the Explore, the A1 is equipped with a woofer and a tweeter.
This is not the case with the Beosound Explore. It's equipped with two pieces of full range drivers, which provides a little worse sound quality.
It's actually the Explore that is closer to a standard speaker anatomy. And it's the A1 that exceeds the expectations and sets a whole new standard for small bluetooth speakers.
By the way, I've partnered up with an Acoustics and Audio Engineering PhD to build a free, simple, 2D, online, mobile compatible speaker placement calculator. It doesn't work that well with small speakers like this - but you still might use it in the future. Just wanted to share.
For something so tiny (it can literally fit on the palm of your hand!), Beosound A1 comes with a 3.5" woofer and a 3/5" tweeter. These specs are far more superior to its competitors, and make the A1 shine through.
Design and Build
Both Bluetooth speakers are very small and have chic-looking designs. The materials used for the Beosound Explore, in particular, are made for it to last in harsher weather conditions because this speaker is meant to be outdoors. The materials are both water-resistant and rust-proof.
The Beosound A1, in contrast, is also made from high-caliber materials, which are built to last.
But because Beosound Explore has better materials to withstand weather, it's the winner in design-build.
Connectivity
Both Beosound Explore and A1 can be connected to Bluetooth. Note that the Beosound A1 does have limitations when it comes to Google assistant connections which makes it a wee bit painful, especially that this portable Bluetooth speaker is designed for indoor settings.
Beosound Explore has the same issue, but why would you need a Google assistant when hiking up a mountain? In this scenario, Beosound Explore wins this round.
Conclusion
It boils down to your own needs and preferences.
If you want a Bluetooth speaker for the great outdoors, go with the Explore. If you're going to be doing literally anything else, get the A1.
Lastly, before you buy, make sure checking out the comparison between Beosound Explore and Beosound A1.
Some good reviews of both: