Medium-density fiberboard (MDF) display racks can be suitable for use as countertop racks depending on several factors, but there are some considerations to keep in mind:

1. **Weight Capacity**: MDF is not as strong as materials like metal or solid wood, so you need to consider the weight of the items you'll be displaying on the countertop rack. If you plan to display heavy items, such as large countertop appliances or multiple products, MDF may not provide sufficient support and could risk bowing or breaking under the weight.

2. **Durability**: While MDF is relatively durable, it's not as resilient as materials like metal or solid wood. Countertop racks are subject to frequent use and potential spills or impacts, so you'll want to ensure that the MDF display rack is adequately sealed and finished to resist moisture, scratches, and wear over time.

3. **Stability**: MDF display racks may not offer the same level of stability as racks made from heavier materials. Consider the design of the rack, including its base and overall structure, to ensure that it remains stable and secure on the countertop, especially if it will be holding tall or top-heavy items.

4. **Aesthetics**: MDF can be easily painted, laminated, or finished to achieve a wide range of aesthetics, making it suitable for countertop racks where appearance is important. Choose finishes that complement your branding and enhance the visual appeal of your products.

5. **Cost**: MDF display racks are often more affordable than racks made from solid wood or metal, which can be advantageous if you're working within a tight budget. However, consider the long-term cost-effectiveness of MDF in terms of durability and maintenance requirements.

6. **Maintenance**: MDF is susceptible to water damage and may warp or swell if exposed to moisture for extended periods. To maintain the integrity of the countertop rack, be sure to clean up spills promptly and avoid placing hot or wet items directly on the surface.

Ultimately, whether an MDF display rack is suitable for use as a countertop rack depends on your specific needs, preferences, and the nature of the items you'll be displaying. If you're unsure, consider consulting with a manufacturer or supplier who can advise you on the best materials and design options for your countertop display rack.