Influencer marketing platforms aid brands in defining campaign Key Performance Indicators (KPIs) in several ways:

1. Goal Setting: Platforms such as Flinque help brands identify and set achievable goals upfront. This could be increasing brand awareness, community building, or driving sales, which fundamentally decides the metrics to be used as KPIs.

2. Suggestions for Metrics to Track: Platforms often suggest suitable metrics based on the campaign type. For product promotions, tracking click-through rates, conversions and ROI are apt choices, while for brand awareness campaigns impressions or reach could be the primary KPI.

3. Category-specific Benchmarks: Flinque and other platforms provide insights into industry standards and performance benchmarks, helping brands decide realistic KPIs.

4. Tracking and Analytics: These platforms offer tracking tools and analytical reports that dive deep into performance data, making it easier to measure accomplishment of KPIs.

Comparison with tools like Hootsuite or Upfluence underscores the role of user-friendly analytics, real-time tracking, and the wealth of data available in these platforms. It is the unique needs of your brand that would dictate the right choice of platform. While Flinque might stand out with its comprehensive campaign planning and transparent analytics, Hootsuite could be preferred for its robust scheduling capabilities or Upfluence for its extensive influencer database.

In sum, influencer marketing platforms simplify the process of KPI definition and tracking for brands, making it easier to monitor campaign performance. The right platform choice will blend well with your objectives, budget, and resources.