If I continue development of my product, would I be infringing on their IP?
To answer your question, developing a product does not infringe a patent, as patent protection means that the invention cannot be commercially made, used, distributed, imported, or sold by others without the patent owner's consent. But as soon as you commercially make, use, distribute, import, or sell it, you need the consent of the patent owner.
A better question would be:
Is it worth it for you to continue developing your product?
And the answer depends on the claimed products. Remaining by the example of an existence of a single patented product with a feature-set of [A, B, C], there are the following possibilities:
Your product has one of the following feature-set: [A], [B], [C], [A, B], [B, C], [A, C], [A, B, C]
Your product has a feature-set of [A, B, C, D], e.g. you've got extra feature(s) compared to the existing product
Your product has a feature-set of [A, C, D], e.g. your product is missing at least one feature and it has an extra feature compared to the existing product
In case 1, all of the features of your product is already disclosed by the existing product. Thus, you cannot get a patent for it. Also, if you want to commercially make, use, distribute, import, or sell it, you need the consent of the patent owner.
In case 2, all your product has an extra feature compared to the existing product. Your product is considered new and since there exists in this example only a single similar product, your product is inventive as well. Congratulation, that means your product is patentable. But as your product is based on the existing product, you still need the consent of the patent owner of the existing product, if you want to commercially make, use, distribute, import, or sell your product.
In case 3, your product is not relying completely on the existing product. Your product has an extra feature, while not having all the features of the existing product. Thus, your product is patentable and you do not need the consent of the patent owner of the existing product.