The Edinburgh-based consultancy firm conducted a due diligence exercise with a fake financial advice firm as part of its latest Platform Market Scorecard report.
Its research highlighted the "increasing difficulties" of a single platform being suitable for every client on an advice firm's books.
A solution of having a small number of platforms for each client segment - for example depending on the level of assets the client had - would also address the difficulty of assessing each of the 20-odd platforms in the market for every client.
Steven Nelson, head of research at the Lang Cat, said: "Due diligence remains a key issue for everyone in the sector, whether you’re a platform or an adviser.
"With 20-plus intermediated platforms to choose from, it’s impossible and impractical for advisory firms to assess each one for every client. Yet many tools and adviser services are set up to encourage this very way of working.
"There needs to be a robust and defensible process of creating a manageable panel that meets client and adviser requirements but is also realistically priced for what it does. Cheapest does not mean best, something cheap and unsuitable is still unsuitable."
The analysis the Lang Cat did with its fake financial advice firm - called the Long Dog, based on having 40 clients with average model portfolios of £350,000 and all but one with a moderate to high weighting in a pension wrapper - showed some platforms were better for clients with different levels of assets.
First, the company whittled all platforms on the market down to a longlist of seven based on their technology, functionality, products and tools, before assessing their charges.
For example based on platform charges the Lang Cat found Nucleus or Elevate would be better options for more modest portfolio sizes, Transact and Zurich were better for medium-sized multi-wrapper portfolios but AJ Bell was a more natural option for medium-to-high sized portfolios.
Based on its analysis, the Lang Cat came to the conclusion it would be "ludicrous" to assess each client on price against each platform, but advisers felt under pressure to do so.
It recommended creating a "strategic platform panel" after carrying out proposition suitability first, so clients would naturally fit into one of the platforms, but it warned against this becoming a "reflexive" choice.
Mr Nelson added that Mifid II product governance rules (PROD), which came into effect in January, highlighted the importance of advisers segmenting their clients.
The product governance rules of Mifid II include requirements that manufacturers and distributors of products get to know their target markets.
This means advisers will have to consider which target market a product is likely to be suitable for, have a distribution strategy for their target market and review the products they offer regularly.
Mr Nelson said: "Post PROD, there is an emerging view that firms should approach platform selection separately for each client segment. It is something that all firms now need to take into consideration. Exercises of this type are complex, even when you simplify them.
"As we worked through this exercise, we began to wonder whether the due diligence model needs some major surgery. We think we can demonstrate this is a much more effective way to assess pricing than having to run each client against each platform in the market.
"As absurd as that sounds, it’s the way many of the tools and systems designed to support advisers are set up. Our view is that creating a strategic platform panel, where proposition, financial performance and price are all threaded through is the way to go. And we believe this works well with the market and regulatory environment as it is today."
Scott Gallacher, director of Rowley Turton, said: "When we go through a due diligence exercise we tend to do it about once a year and we pick three or four sample clients and use those as a base.
"The principle of what the Lang Cat has said is sound but I would hope that all advisers would do this. We find we tend to accumulate platforms because we are independent financial advisers we don't shoehorn people.
"Using one platforms works if your clients are all very much the same, with similar ages, similar attitudes to risk and similar investment amounts."